diff --git a/pyproject.toml b/pyproject.toml
index 6619e1c75..129a4dfb8 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "poetry.core.masonry.api"
 
 [tool.poetry]
 name = "writer"
-version = "0.8.0rc7"
+version = "0.8.0rc8"
 description = "An open-source, Python framework for building feature-rich apps that are fully integrated with the Writer platform."
 authors = ["Writer, Inc."]
 readme = "README.md"
diff --git a/src/ui/public/components/workflows_writeraddtokg.svg b/src/ui/public/components/workflows_writeraddtokg.svg
new file mode 100644
index 000000000..2ef070cb9
--- /dev/null
+++ b/src/ui/public/components/workflows_writeraddtokg.svg
@@ -0,0 +1,11 @@
+<svg width="18" height="18" viewBox="0 0 18 18" fill="none" xmlns="http://www.w3.org/2000/svg">
+<rect width="18" height="18" rx="4" fill="#333333"/>
+<g clip-path="url(#clip0_23670_312740)">
+<path fill-rule="evenodd" clip-rule="evenodd" d="M12.2413 5.74087C12.589 5.74087 12.8709 5.45897 12.8709 5.11124C12.8709 4.7635 12.589 4.48161 12.2413 4.48161C11.8935 4.48161 11.6117 4.7635 11.6117 5.11124C11.6117 5.45897 11.8935 5.74087 12.2413 5.74087ZM12.2413 6.40753C12.9572 6.40753 13.5376 5.82716 13.5376 5.11124C13.5376 4.39531 12.9572 3.81494 12.2413 3.81494C11.6033 3.81494 11.073 4.27579 10.9651 4.88274L9.37497 5.41277C9.03569 4.84401 8.41427 4.46305 7.70388 4.46305C6.63 4.46305 5.75944 5.33361 5.75944 6.4075C5.75944 6.70796 5.82759 6.99251 5.94928 7.24652L5.23628 7.95952C5.02045 7.79896 4.75297 7.70394 4.46329 7.70394C3.74736 7.70394 3.16699 8.28431 3.16699 9.00024C3.16699 9.71616 3.74736 10.2965 4.46329 10.2965C4.66612 10.2965 4.85808 10.2499 5.02903 10.1669L5.50373 10.6416C5.25629 11.005 5.11165 11.444 5.11165 11.9168C5.11165 13.1697 6.1273 14.1853 7.38017 14.1853C8.63304 14.1853 9.64869 13.1697 9.64869 11.9168C9.64869 11.7161 9.62262 11.5215 9.57369 11.3361L10.4855 10.8802C10.8356 11.6812 11.635 12.241 12.5651 12.241C13.8179 12.241 14.8336 11.2253 14.8336 9.97246C14.8336 8.71959 13.8179 7.70394 12.5651 7.70394C12.0649 7.70394 11.6026 7.86578 11.2276 8.13996L9.54949 7.02122C9.61361 6.8283 9.64833 6.62195 9.64833 6.4075C9.64833 6.28052 9.63616 6.15638 9.61292 6.03618L11.0266 5.56495C11.2105 6.05711 11.685 6.40753 12.2413 6.40753ZM5.95594 10.151C6.34528 9.83656 6.84074 9.64827 7.38017 9.64827C7.42048 9.64827 7.46054 9.64933 7.50033 9.6514V8.34141C7.05141 8.29471 6.64788 8.09527 6.34264 7.79597L5.65329 8.48532C5.72168 8.64316 5.75958 8.81727 5.75958 9.00024C5.75958 9.27083 5.67667 9.52207 5.53487 9.72991L5.95594 10.151ZM8.16699 9.78844V8.29645C8.59487 8.19191 8.96723 7.94578 9.2316 7.61052L10.7443 8.61902C10.463 8.99684 10.2965 9.46521 10.2965 9.97246C10.2965 10.057 10.3012 10.1404 10.3102 10.2225L9.30946 10.7229C9.04525 10.2968 8.64386 9.9648 8.16699 9.78844ZM4.46329 9.62986C4.81102 9.62986 5.09292 9.34797 5.09292 9.00024C5.09292 8.6525 4.81102 8.37061 4.46329 8.37061C4.11555 8.37061 3.83366 8.6525 3.83366 9.00024C3.83366 9.34797 4.11555 9.62986 4.46329 9.62986ZM14.1669 9.97246C14.1669 10.8571 13.4497 11.5743 12.5651 11.5743C11.6804 11.5743 10.9632 10.8571 10.9632 9.97246C10.9632 9.08778 11.6804 8.37061 12.5651 8.37061C13.4497 8.37061 14.1669 9.08778 14.1669 9.97246ZM7.70388 7.68528C8.40958 7.68528 8.98166 7.11319 8.98166 6.4075C8.98166 5.7018 8.40958 5.12972 7.70388 5.12972C6.99819 5.12972 6.42611 5.7018 6.42611 6.4075C6.42611 7.11319 6.99819 7.68528 7.70388 7.68528ZM8.98202 11.9168C8.98202 12.8015 8.26485 13.5186 7.38017 13.5186C6.49549 13.5186 5.77832 12.8015 5.77832 11.9168C5.77832 11.0321 6.49549 10.3149 7.38017 10.3149C8.26485 10.3149 8.98202 11.0321 8.98202 11.9168Z" fill="white"/>
+</g>
+<defs>
+<clipPath id="clip0_23670_312740">
+<rect width="12" height="12" fill="white" transform="translate(3 3)"/>
+</clipPath>
+</defs>
+</svg>
diff --git a/src/ui/src/builder/BuilderApp.vue b/src/ui/src/builder/BuilderApp.vue
index d1980d562..5f4162a71 100644
--- a/src/ui/src/builder/BuilderApp.vue
+++ b/src/ui/src/builder/BuilderApp.vue
@@ -105,31 +105,34 @@ import { isPlatformMac } from "../core/detectPlatform";
 import BuilderHeader from "./BuilderHeader.vue";
 import BuilderTooltip from "./BuilderTooltip.vue";
 import BuilderComponentShortcuts from "./BuilderComponentShortcuts.vue";
+import BuilderAsyncLoader from "./BuilderAsyncLoader.vue";
+import BuilderCodePanel from "./BuilderCodePanel.vue";
+import BuilderLogPanel from "./BuilderLogPanel.vue";
 
-const BuilderSettings = defineAsyncComponent(
-	() => import("./BuilderSettings.vue"),
-);
-const BuilderSidebar = defineAsyncComponent(
-	() => import("./BuilderSidebar.vue"),
-);
-const ComponentRenderer = defineAsyncComponent(
-	() => import("@/renderer/ComponentRenderer.vue"),
-);
-const BuilderInstanceTracker = defineAsyncComponent(
-	() => import("./BuilderInstanceTracker.vue"),
-);
-const BuilderInsertionOverlay = defineAsyncComponent(
-	() => import("./BuilderInsertionOverlay.vue"),
-);
-const BuilderInsertionLabel = defineAsyncComponent(
-	() => import("./BuilderInsertionLabel.vue"),
-);
-const BuilderCodePanel = defineAsyncComponent(
-	() => import("./BuilderCodePanel.vue"),
-);
-const BuilderLogPanel = defineAsyncComponent(
-	() => import("./BuilderLogPanel.vue"),
-);
+const BuilderSettings = defineAsyncComponent({
+	loader: () => import("./BuilderSettings.vue"),
+	loadingComponent: BuilderAsyncLoader,
+});
+const BuilderSidebar = defineAsyncComponent({
+	loader: () => import("./BuilderSidebar.vue"),
+	loadingComponent: BuilderAsyncLoader,
+});
+const ComponentRenderer = defineAsyncComponent({
+	loader: () => import("@/renderer/ComponentRenderer.vue"),
+	loadingComponent: BuilderAsyncLoader,
+});
+const BuilderInstanceTracker = defineAsyncComponent({
+	loader: () => import("./BuilderInstanceTracker.vue"),
+	loadingComponent: BuilderAsyncLoader,
+});
+const BuilderInsertionOverlay = defineAsyncComponent({
+	loader: () => import("./BuilderInsertionOverlay.vue"),
+	loadingComponent: BuilderAsyncLoader,
+});
+const BuilderInsertionLabel = defineAsyncComponent({
+	loader: () => import("./BuilderInsertionLabel.vue"),
+	loadingComponent: BuilderAsyncLoader,
+});
 
 const wf = inject(injectionKeys.core);
 const ssbm = inject(injectionKeys.builderManager);
diff --git a/src/ui/src/builder/BuilderAsyncLoader.vue b/src/ui/src/builder/BuilderAsyncLoader.vue
new file mode 100644
index 000000000..27fb46e68
--- /dev/null
+++ b/src/ui/src/builder/BuilderAsyncLoader.vue
@@ -0,0 +1,19 @@
+<template>
+	<div class="BuilderAsyncLoader">
+		<LoadingSymbol />
+	</div>
+</template>
+
+<script setup lang="ts">
+import LoadingSymbol from "@/renderer/LoadingSymbol.vue";
+</script>
+
+<style scoped>
+.BuilderAsyncLoader {
+	width: 100%;
+	height: 100%;
+	display: flex;
+	align-items: center;
+	justify-content: center;
+}
+</style>
diff --git a/src/ui/src/builder/BuilderCodePanel.vue b/src/ui/src/builder/BuilderCodePanel.vue
index 78394bac1..2b7e329ee 100644
--- a/src/ui/src/builder/BuilderCodePanel.vue
+++ b/src/ui/src/builder/BuilderCodePanel.vue
@@ -17,11 +17,16 @@
 </template>
 
 <script setup lang="ts">
-import { computed, inject, ref, watch } from "vue";
-import BuilderEmbeddedCodeEditor from "./BuilderEmbeddedCodeEditor.vue";
+import { computed, defineAsyncComponent, inject, ref, watch } from "vue";
 import BuilderPanel, { type BuilderPanelAction } from "./BuilderPanel.vue";
+import BuilderAsyncLoader from "./BuilderAsyncLoader.vue";
 import injectionKeys from "@/injectionKeys";
 
+const BuilderEmbeddedCodeEditor = defineAsyncComponent({
+	loader: () => import("./BuilderEmbeddedCodeEditor.vue"),
+	loadingComponent: BuilderAsyncLoader,
+});
+
 const wf = inject(injectionKeys.core);
 
 const wfbm = inject(injectionKeys.builderManager);
diff --git a/src/ui/src/builder/BuilderHeader.vue b/src/ui/src/builder/BuilderHeader.vue
index 09cc97e85..a2be0bf07 100644
--- a/src/ui/src/builder/BuilderHeader.vue
+++ b/src/ui/src/builder/BuilderHeader.vue
@@ -49,7 +49,7 @@
 			variant="primary"
 			size="small"
 			class="panelToggler"
-			title="Toggle Code panel"
+			data-automation-action="toggle-code-panel"
 			:class="{ active: ssbm.openPanels.has('code') }"
 			@click="togglePanel('code')"
 		>
@@ -60,6 +60,7 @@
 			variant="primary"
 			size="small"
 			class="panelToggler"
+			data-automation-action="toggle-log-panel"
 			title="Toggle Log panel"
 			:class="{ active: ssbm.openPanels.has('log') }"
 			@click="togglePanel('log')"
diff --git a/src/ui/src/builder/BuilderLogWorkflowExecution.vue b/src/ui/src/builder/BuilderLogWorkflowExecution.vue
index 6a5a3f266..133fa97a2 100644
--- a/src/ui/src/builder/BuilderLogWorkflowExecution.vue
+++ b/src/ui/src/builder/BuilderLogWorkflowExecution.vue
@@ -31,10 +31,10 @@
 				</div>
 				<div class="result">
 					<BuilderModal
-						v-if="displayedDetails !== null"
+						v-if="displayedItemId == itemId"
 						:close-action="{
 							desc: 'Close',
-							fn: () => (displayedDetails = null),
+							fn: () => (displayedItemId = null),
 						}"
 						icon="find_in_page"
 						modal-title="Details"
@@ -48,10 +48,10 @@
 									environment of the direct dependents of this
 									block. There, it's accessible via @{result}.
 								</p>
-								<div class="data">
+								<div class="data" data-automation-key="result">
 									<SharedJsonViewer
-										v-if="displayedDetails?.result"
-										:data="displayedDetails.result"
+										v-if="item?.result"
+										:data="item.result"
 										:initial-depth="1"
 										class="data"
 									/>
@@ -68,12 +68,8 @@
 								</p>
 								<div class="data">
 									<SharedJsonViewer
-										v-if="
-											displayedDetails?.executionEnvironment
-										"
-										:data="
-											displayedDetails.executionEnvironment
-										"
+										v-if="item?.executionEnvironment"
+										:data="item.executionEnvironment"
 										:initial-depth="1"
 										class="data"
 									/>
@@ -89,10 +85,13 @@
 									determine the result of 'Run workflow'
 									blocks and 'Chat completion' tool calls.
 								</p>
-								<div class="data">
+								<div
+									class="data"
+									data-automation-key="return-value"
+								>
 									<SharedJsonViewer
-										v-if="displayedDetails?.returnValue"
-										:data="displayedDetails.returnValue"
+										v-if="item?.returnValue"
+										:data="item.returnValue"
 										:initial-depth="1"
 										class="data"
 									/>
@@ -111,15 +110,7 @@
 						"
 						variant="secondary"
 						size="small"
-						@click="
-							() =>
-								(displayedDetails = {
-									executionEnvironment:
-										item.executionEnvironment,
-									result: item.result,
-									returnValue: item.returnValue,
-								})
-						"
+						@click="() => (displayedItemId = itemId)"
 					>
 						<i class="material-symbols-outlined">find_in_page</i>
 						Details
@@ -128,12 +119,18 @@
 				<div class="time">
 					{{ formatExecutionTime(item.executionTimeInSeconds) }}
 				</div>
+				<div
+					v-if="item.message"
+					v-dompurify-html="marked.parse(item.message)"
+					class="message markdown"
+				></div>
 			</div>
 		</div>
 	</div>
 </template>
 
 <script setup lang="ts">
+import { marked } from "marked";
 import injectionKeys from "@/injectionKeys";
 import { WorkflowExecutionLog } from "./builderManager";
 import { computed, inject, nextTick, ref } from "vue";
@@ -151,7 +148,7 @@ const { goToComponentParentPage } = useComponentActions(wf, wfbm);
 const props = defineProps<{
 	executionLog: WorkflowExecutionLog;
 }>();
-const displayedDetails = ref(null);
+const displayedItemId = ref<number | null>(null);
 
 type EnrichedExecutionLog = WorkflowExecutionLog & {
 	summary: {
@@ -239,7 +236,7 @@ function formatExecutionTime(timeInSeconds: number): string {
 	grid-row: 1 / 3;
 	display: grid;
 	grid-template-columns: 1fr 1fr 1fr 80px;
-	grid-template-rows: 1fr;
+	grid-template-rows: 1fr auto;
 	align-items: center;
 	padding: 8px;
 	border-radius: 6px;
@@ -290,6 +287,12 @@ function formatExecutionTime(timeInSeconds: number): string {
 	grid-row: 1 / 2;
 }
 
+.item .message {
+	grid-column: 1 / 5;
+	grid-row: 2 / 3;
+	margin-top: 8px;
+}
+
 .detailsModalContent {
 	display: flex;
 	flex-direction: column;
@@ -308,4 +311,11 @@ function formatExecutionTime(timeInSeconds: number): string {
 	margin-top: 8px;
 	font-size: 14px;
 }
+
+.markdown :deep(code) {
+	font-family: monospace;
+	font-size: 13px;
+	background-color: rgba(0, 0, 0, 0.05);
+	padding: 2px;
+}
 </style>
diff --git a/src/ui/src/builder/BuilderSettings.vue b/src/ui/src/builder/BuilderSettings.vue
index d514b7ed1..c8d88311e 100644
--- a/src/ui/src/builder/BuilderSettings.vue
+++ b/src/ui/src/builder/BuilderSettings.vue
@@ -19,7 +19,7 @@
 				class="windowAction"
 				tabindex="0"
 				title="Close (Esc)"
-				data-automation-action="close"
+				data-automation-action="close-settings"
 				@click="closeSettings"
 			>
 				<i class="material-symbols-outlined">close</i>
@@ -68,14 +68,19 @@
 
 <script setup lang="ts">
 import { marked } from "marked";
-import { inject, computed, ref, watch } from "vue";
+import { inject, computed, ref, watch, defineAsyncComponent } from "vue";
 import injectionKeys from "../injectionKeys";
 
-import BuilderSettingsHandlers from "./BuilderSettingsHandlers.vue";
 import BuilderSettingsProperties from "./BuilderSettingsProperties.vue";
 import BuilderSettingsBinding from "./BuilderSettingsBinding.vue";
 import BuilderSettingsVisibility from "./BuilderSettingsVisibility.vue";
 import BuilderCopyText from "./BuilderCopyText.vue";
+import BuilderAsyncLoader from "./BuilderAsyncLoader.vue";
+
+const BuilderSettingsHandlers = defineAsyncComponent({
+	loader: () => import("./BuilderSettingsHandlers.vue"),
+	loadingComponent: BuilderAsyncLoader,
+});
 
 const wf = inject(injectionKeys.core);
 const ssbm = inject(injectionKeys.builderManager);
diff --git a/src/ui/src/builder/BuilderSidebarTree.vue b/src/ui/src/builder/BuilderSidebarTree.vue
index 9b41af95d..c03a028af 100644
--- a/src/ui/src/builder/BuilderSidebarTree.vue
+++ b/src/ui/src/builder/BuilderSidebarTree.vue
@@ -50,11 +50,19 @@
 			</div>
 		</div>
 		<div class="add">
-			<button v-if="rootType == 'root'" @click="addPage">
+			<button
+				v-if="rootType == 'root'"
+				data-automation-action="add-page"
+				@click="addPage"
+			>
 				<i class="material-symbols-outlined"> add </i>
 				Add Page
 			</button>
-			<button v-if="rootType == 'workflows_root'" @click="addWorkflow">
+			<button
+				v-if="rootType == 'workflows_root'"
+				data-automation-action="add-workflow"
+				@click="addWorkflow"
+			>
 				<i class="material-symbols-outlined"> add </i>
 				Add Workflow
 			</button>
diff --git a/src/ui/src/builder/BuilderSwitcher.vue b/src/ui/src/builder/BuilderSwitcher.vue
index 2b0e4ccc2..7a3cf597d 100644
--- a/src/ui/src/builder/BuilderSwitcher.vue
+++ b/src/ui/src/builder/BuilderSwitcher.vue
@@ -1,11 +1,16 @@
 <template>
 	<div class="BuilderSwitcher">
-		<div :class="{ active: activeId == 'ui' }" @click="selectOption('ui')">
+		<div
+			data-automation-action="set-mode-ui"
+			:class="{ active: activeId == 'ui' }"
+			@click="selectOption('ui')"
+		>
 			<i class="icon material-symbols-outlined"> brush </i>
 			UI
 		</div>
 		<div
 			v-if="isWorkflowsFeatureFlagged"
+			data-automation-action="set-mode-workflows"
 			:class="{ active: activeId == 'workflows' }"
 			@click="selectOption('workflows')"
 		>
@@ -14,6 +19,7 @@
 		</div>
 		<div
 			:class="{ active: activeId == 'preview' }"
+			data-automation-action="set-mode-preview"
 			@click="selectOption('preview')"
 		>
 			<i class="icon material-symbols-outlined"> preview </i>
diff --git a/src/ui/src/builder/builderManager.ts b/src/ui/src/builder/builderManager.ts
index b3e86336a..e6c88cd2d 100644
--- a/src/ui/src/builder/builderManager.ts
+++ b/src/ui/src/builder/builderManager.ts
@@ -18,6 +18,7 @@ export type WorkflowExecutionLog = {
 	summary: {
 		componentId: Component["id"];
 		outcome: string;
+		message?: string;
 		executionTimeInSeconds: number;
 		// eslint-disable-next-line @typescript-eslint/no-explicit-any
 		result: any;
diff --git a/src/ui/src/components/core/content/CoreChatBot/CoreChatbotAvatar.vue b/src/ui/src/components/core/content/CoreChatBot/CoreChatbotAvatar.vue
new file mode 100644
index 000000000..b7c90280e
--- /dev/null
+++ b/src/ui/src/components/core/content/CoreChatBot/CoreChatbotAvatar.vue
@@ -0,0 +1,28 @@
+<template>
+	<div class="CoreChatbotAvatar">{{ initials }}</div>
+</template>
+
+<script lang="ts" setup>
+defineProps({
+	initials: { type: String, required: true },
+});
+</script>
+
+<style scoped>
+.CoreChatbotAvatar {
+	border-radius: 50%;
+	background: var(--avatarBackgroundColor);
+	color: var(--avatarTextColor);
+	margin-top: 6px;
+	height: 32px;
+	width: 32px;
+	flex: 0 0 32px;
+	display: flex;
+	font-weight: 500;
+	font-size: 0.75rem;
+	align-items: center;
+	justify-content: center;
+	overflow: hidden;
+	text-transform: uppercase;
+}
+</style>
diff --git a/src/ui/src/components/core/content/CoreChatBot/CoreChatbotLoader.vue b/src/ui/src/components/core/content/CoreChatBot/CoreChatbotLoader.vue
new file mode 100644
index 000000000..2978722e8
--- /dev/null
+++ b/src/ui/src/components/core/content/CoreChatBot/CoreChatbotLoader.vue
@@ -0,0 +1,65 @@
+<template>
+	<div class="CoreChatbotLoader" :style="{ '--dotSize': '6px' }">
+		<span class="CoreChatbotLoader__dot"></span>
+		<span class="CoreChatbotLoader__dot"></span>
+		<span class="CoreChatbotLoader__dot"></span>
+	</div>
+</template>
+
+<style scoped>
+.CoreChatbotLoader {
+	width: 100px;
+	height: 100%;
+	display: flex;
+	gap: var(--dotSize);
+	align-items: center;
+	justify-content: center;
+}
+
+.CoreChatbotLoader__dot {
+	display: inline-block;
+	width: var(--dotSize);
+	height: var(--dotSize);
+	position: relative;
+}
+
+.CoreChatbotLoader__dot::after {
+	display: inline-block;
+	content: "";
+	position: absolute;
+	background-color: currentColor;
+	width: calc(var(--dotSize) / 2);
+	height: calc(var(--dotSize) / 2);
+	border-radius: 50%;
+	animation: changeSize 1.5s infinite;
+
+	top: 50%;
+	left: 50%;
+	transform: translate(-50%, -50%);
+}
+
+.CoreChatbotLoader__dot:nth-child(1)::after {
+	animation-delay: 0s;
+}
+.CoreChatbotLoader__dot:nth-child(2)::after {
+	animation-delay: 0.5s;
+}
+.CoreChatbotLoader__dot:nth-child(3)::after {
+	animation-delay: 1s;
+}
+
+@keyframes changeSize {
+	0% {
+		width: calc(var(--dotSize) / 2);
+		height: calc(var(--dotSize) / 2);
+	}
+	50% {
+		width: var(--dotSize);
+		height: var(--dotSize);
+	}
+	100% {
+		width: calc(var(--dotSize) / 2);
+		height: calc(var(--dotSize) / 2);
+	}
+}
+</style>
diff --git a/src/ui/src/components/core/content/CoreChatBot/CoreChatbotMessage.vue b/src/ui/src/components/core/content/CoreChatBot/CoreChatbotMessage.vue
new file mode 100644
index 000000000..ad8c48cc5
--- /dev/null
+++ b/src/ui/src/components/core/content/CoreChatBot/CoreChatbotMessage.vue
@@ -0,0 +1,160 @@
+<template>
+	<div class="CoreChatbotMessage" :aria-busy="isLoading">
+		<CoreChatbotAvatar :initials="initials" />
+		<div
+			class="CoreChatbotMessage__content"
+			:style="{ background: contentBgColor }"
+		>
+			<CoreChatbotLoader v-if="displayLoader" />
+			<div v-else class="CoreChatbotMessage__content__text">
+				<BaseMarkdown v-if="useMarkdown" :raw-text="content">
+				</BaseMarkdown>
+				<template v-else>
+					{{ content }}
+				</template>
+			</div>
+			<div
+				v-if="actions.length"
+				class="CoreChatbotMessage__content__actions"
+			>
+				<button
+					v-for="(action, actionIndex) in actions"
+					:key="actionIndex"
+					class="action"
+					@click="$emit('actionClick', action)"
+				>
+					<div v-if="action.subheading" class="subheading">
+						{{ action.subheading }}
+					</div>
+					<h3 class="name">{{ action.name }}</h3>
+					<div v-if="action.desc" class="desc">
+						{{ action.desc }}
+					</div>
+				</button>
+			</div>
+		</div>
+	</div>
+</template>
+
+<script lang="ts">
+export type Action = {
+	subheading?: string;
+	name: string;
+	desc?: string;
+	data?: string;
+};
+
+export type Message = {
+	role: string;
+	pending: boolean;
+	content: string;
+	actions?: Action[];
+};
+</script>
+
+<script lang="ts" setup>
+import { computed, defineAsyncComponent, PropType } from "vue";
+import CoreChatbotAvatar from "./CoreChatbotAvatar.vue";
+
+const BaseMarkdown = defineAsyncComponent(
+	() => import("../../base/BaseMarkdown.vue"),
+);
+const CoreChatbotLoader = defineAsyncComponent(
+	() => import("./CoreChatbotLoader.vue"),
+);
+
+const props = defineProps({
+	initials: { type: String, required: true },
+	useMarkdown: { type: Boolean, required: false },
+	message: {
+		type: Object as PropType<Message>,
+		required: false,
+		default: undefined,
+	},
+	assistantRoleColor: { type: String, required: false, default: "" },
+	isLoading: { type: Boolean, required: false },
+});
+
+defineEmits({
+	actionClick: (action: Action) =>
+		typeof action === "object" && action !== null,
+});
+
+const actions = computed<Action[]>(() => props.message?.actions ?? []);
+
+const displayLoader = computed(() => {
+	return props.isLoading && !content.value;
+});
+
+const role = computed(() => {
+	if (props.isLoading) return "assistant";
+	return props.message?.role ?? "";
+});
+
+const content = computed(() => props.message?.content.trim() ?? "");
+
+const contentBgColor = computed(() => {
+	switch (role.value) {
+		case "user":
+			return "var(--userRoleColor)";
+		case "assistant":
+			return (
+				props.assistantRoleColor ||
+				"linear-gradient(264deg, #f5ebff 0.71%, #eef1ff 100%)"
+			);
+		default:
+			return "";
+	}
+});
+</script>
+
+<style scoped>
+.CoreChatbotMessage {
+	display: flex;
+	gap: 8px;
+}
+
+.CoreChatbotMessage__content {
+	border-radius: 8px;
+	width: fit-content;
+	flex: 0 1 auto;
+	color: var(--primaryTextColor);
+	white-space: pre-wrap;
+}
+
+.CoreChatbotMessage__content__text {
+	line-height: 2;
+	padding: 12px 16px 12px 16px;
+}
+
+.CoreChatbotMessage__content__actions {
+	padding: 16px;
+	background: rgba(0, 0, 0, 0.02);
+	display: flex;
+	gap: 12px;
+	flex-wrap: wrap;
+}
+
+.CoreChatbotMessage__content__actions .action {
+	padding: 12px;
+	border-radius: 4px;
+	background: var(--containerBackgroundColor);
+	overflow: hidden;
+	line-height: normal;
+	display: flex;
+	gap: 4px;
+	flex-direction: column;
+	box-shadow: 0 2px 2px 0px rgba(0, 0, 0, 0.1);
+	cursor: pointer;
+	border: 0;
+}
+
+.action .subheading {
+	color: var(--secondaryTextColor);
+	font-size: 0.7rem;
+}
+
+.action .desc {
+	font-size: 0.7rem;
+}
+</style>
diff --git a/src/ui/src/components/core/content/CoreChatBot/CoreChatbotSentMessageIcon.vue b/src/ui/src/components/core/content/CoreChatBot/CoreChatbotSentMessageIcon.vue
new file mode 100644
index 000000000..a7521894e
--- /dev/null
+++ b/src/ui/src/components/core/content/CoreChatBot/CoreChatbotSentMessageIcon.vue
@@ -0,0 +1,14 @@
+<template>
+	<svg
+		width="15"
+		height="12"
+		viewBox="0 0 15 12"
+		fill="none"
+		xmlns="http://www.w3.org/2000/svg"
+	>
+		<path
+			d="M14.0712 4.50295C14.2882 4.72002 14.2882 5.07197 14.0712 5.28905L10.5337 8.8265C10.3166 9.04357 9.96468 9.04357 9.7476 8.8265C9.53052 8.60942 9.53052 8.25747 9.7476 8.0404L12.892 4.896L9.7476 1.7516C9.53052 1.53452 9.53052 1.18257 9.7476 0.965495C9.96467 0.74842 10.3166 0.74842 10.5337 0.965495L14.0712 4.50295ZM13.6781 5.45185L3.67268 5.45185L3.67268 4.34014L13.6781 4.34014L13.6781 5.45185ZM2.00511 7.11942L2.00511 8.23114L0.893394 8.23114L0.893394 7.11942L2.00511 7.11942ZM3.67268 9.89871L5.52553 9.89871L5.52553 11.0104L3.67268 11.0104L3.67268 9.89871ZM2.00511 8.23114C2.00511 9.15211 2.7517 9.89871 3.67268 9.89871L3.67268 11.0104C2.13772 11.0104 0.893394 9.76609 0.893394 8.23114L2.00511 8.23114ZM3.67268 5.45185C2.7517 5.45185 2.00511 6.19845 2.00511 7.11942L0.893394 7.11942C0.893394 5.58447 2.13772 4.34014 3.67268 4.34014L3.67268 5.45185Z"
+			fill="currentColor"
+		/>
+	</svg>
+</template>
diff --git a/src/ui/src/components/core/content/CoreChatbot.vue b/src/ui/src/components/core/content/CoreChatbot.vue
index cd2c32a56..70064df84 100644
--- a/src/ui/src/components/core/content/CoreChatbot.vue
+++ b/src/ui/src/components/core/content/CoreChatbot.vue
@@ -9,55 +9,24 @@ See the stubs for more details.
 	<div ref="rootEl" class="CoreChatbot">
 		<div ref="messageAreaEl" class="messageArea">
 			<div ref="messagesEl" class="messages">
-				<div
+				<CoreChatbotMessage
 					v-for="(message, messageId) in messages"
 					:key="messageId"
-					class="message"
-					:class="message.role"
-				>
-					<div class="avatar">
-						{{
-							message.role == "assistant"
-								? fields.assistantInitials.value
-								: fields.userInitials.value
-						}}
-					</div>
-					<div class="content">
-						<div class="text">
-							<BaseMarkdown
-								v-if="fields.useMarkdown.value == 'yes'"
-								:raw-text="message.content?.trim()"
-							>
-							</BaseMarkdown>
-							<template v-else>
-								{{ message.content?.trim() }}
-							</template>
-						</div>
-						<div v-if="message.actions" class="actions">
-							<button
-								v-for="(action, actionIndex) in message.actions"
-								:key="actionIndex"
-								class="action"
-								@click="handleActionClick(action)"
-							>
-								<div
-									v-if="action.subheading"
-									class="subheading"
-								>
-									{{ action.subheading }}
-								</div>
-								<h3 class="name">{{ action.name }}</h3>
-								<div v-if="action.desc" class="desc">
-									{{ action.desc }}
-								</div>
-							</button>
-						</div>
-					</div>
-				</div>
-				<div v-if="isResponsePending" class="loadingContainer">
-					<LoadingSymbol class="loadingSymbol"></LoadingSymbol
-					>Loading...
-				</div>
+					:message="message"
+					:use-markdown="fields.useMarkdown.value == 'yes'"
+					:assistant-role-color="fields.assistantRoleColor.value"
+					:initials="
+						message.role === 'assistant'
+							? fields.assistantInitials.value
+							: fields.userInitials.value
+					"
+					@action-click="handleActionClick($event)"
+				/>
+				<CoreChatbotMessage
+					v-if="displayExtraLoader"
+					is-loading
+					:initials="fields.assistantInitials.value"
+				/>
 			</div>
 		</div>
 		<template v-if="files.length > 0">
@@ -112,18 +81,7 @@ See the stubs for more details.
 				title="Send message"
 				@click="handleMessageSent"
 			>
-				<svg
-					width="15"
-					height="12"
-					viewBox="0 0 15 12"
-					fill="none"
-					xmlns="http://www.w3.org/2000/svg"
-				>
-					<path
-						d="M14.0712 4.50295C14.2882 4.72002 14.2882 5.07197 14.0712 5.28905L10.5337 8.8265C10.3166 9.04357 9.96468 9.04357 9.7476 8.8265C9.53052 8.60942 9.53052 8.25747 9.7476 8.0404L12.892 4.896L9.7476 1.7516C9.53052 1.53452 9.53052 1.18257 9.7476 0.965495C9.96467 0.74842 10.3166 0.74842 10.5337 0.965495L14.0712 4.50295ZM13.6781 5.45185L3.67268 5.45185L3.67268 4.34014L13.6781 4.34014L13.6781 5.45185ZM2.00511 7.11942L2.00511 8.23114L0.893394 8.23114L0.893394 7.11942L2.00511 7.11942ZM3.67268 9.89871L5.52553 9.89871L5.52553 11.0104L3.67268 11.0104L3.67268 9.89871ZM2.00511 8.23114C2.00511 9.15211 2.7517 9.89871 3.67268 9.89871L3.67268 11.0104C2.13772 11.0104 0.893394 9.76609 0.893394 8.23114L2.00511 8.23114ZM3.67268 5.45185C2.7517 5.45185 2.00511 6.19845 2.00511 7.11942L0.893394 7.11942C0.893394 5.58447 2.13772 4.34014 3.67268 4.34014L3.67268 5.45185Z"
-						fill="currentColor"
-					/>
-				</svg>
+				<CoreChatbotSentMessageIcon />
 			</WdsControl>
 			<WdsControl
 				v-if="fields.enableFileUpload.value != 'no'"
@@ -138,8 +96,6 @@ See the stubs for more details.
 </template>
 
 <script lang="ts">
-import LoadingSymbol from "@/renderer/LoadingSymbol.vue";
-import BaseMarkdown from "../base/BaseMarkdown.vue";
 import { FieldCategory, FieldType } from "@/writerTypes";
 import {
 	accentColor,
@@ -348,25 +304,14 @@ import {
 	ComputedRef,
 } from "vue";
 import injectionKeys from "@/injectionKeys";
-
-type Action = {
-	subheading?: string;
-	name: string;
-	desc?: string;
-	data?: string;
-};
-
-type Message = {
-	role: string;
-	pending: boolean;
-	content: string;
-	actions?: Action[];
-};
+import CoreChatbotSentMessageIcon from "./CoreChatBot/CoreChatbotSentMessageIcon.vue";
+import CoreChatbotMessage from "./CoreChatBot/CoreChatbotMessage.vue";
+import type { Message } from "./CoreChatBot/CoreChatbotMessage.vue";
 
 const rootEl: Ref<HTMLElement> = ref(null);
 const messageAreaEl: Ref<HTMLElement> = ref(null);
 const messagesEl: Ref<HTMLElement> = ref(null);
-const isResponsePending: Ref<boolean> = ref(false);
+const messageIndexLoading: Ref<number | undefined> = ref(undefined);
 const fields = inject(injectionKeys.evaluatedFields);
 const files: Ref<File[]> = shallowRef([]);
 const isUploadingFiles = ref(false);
@@ -386,9 +331,14 @@ const isUploadSizeExceeded = computed(() => {
 	return filesSize >= MAX_FILE_SIZE;
 });
 
+const displayExtraLoader = computed(() => {
+	if (messageIndexLoading.value === undefined) return false;
+	return messageIndexLoading.value >= messages.value.length;
+});
+
 function handleMessageSent() {
-	if (isResponsePending.value) return;
-	isResponsePending.value = true;
+	if (messageIndexLoading.value) return;
+	messageIndexLoading.value = messages.value.length + 1;
 	const event = new CustomEvent("wf-chatbot-message", {
 		detail: {
 			payload: {
@@ -396,7 +346,7 @@ function handleMessageSent() {
 				content: outgoingMessage.value,
 			},
 			callback: () => {
-				isResponsePending.value = false;
+				messageIndexLoading.value = undefined;
 			},
 		},
 	});
@@ -553,90 +503,6 @@ onBeforeUnmount(() => {
 	flex-direction: column;
 }
 
-.message {
-	display: flex;
-	gap: 8px;
-}
-
-.message .avatar {
-	border-radius: 50%;
-	background: var(--avatarBackgroundColor);
-	color: var(--avatarTextColor);
-	margin-top: 6px;
-	height: 32px;
-	width: 32px;
-	flex: 0 0 32px;
-	display: flex;
-	font-weight: 500;
-	font-size: 0.75rem;
-	align-items: center;
-	justify-content: center;
-	overflow: hidden;
-	text-transform: uppercase;
-}
-
-.message .content {
-	border-radius: 8px;
-	width: fit-content;
-	flex: 0 1 auto;
-	color: var(--primaryTextColor);
-	white-space: pre-wrap;
-}
-
-.message.assistant .content {
-	background: v-bind(
-		"fields.assistantRoleColor.value ? fields.assistantRoleColor.value : 'linear-gradient(264deg, #f5ebff 0.71%, #eef1ff 100%)'"
-	);
-}
-
-.message.user .content {
-	background: var(--userRoleColor);
-}
-
-.content .text {
-	line-height: 2;
-	padding: 12px 16px 12px 16px;
-}
-
-.content .actions {
-	padding: 16px;
-	background: rgba(0, 0, 0, 0.02);
-	display: flex;
-	gap: 12px;
-	flex-wrap: wrap;
-}
-
-.content .actions .action {
-	padding: 12px;
-	border-radius: 4px;
-	background: var(--containerBackgroundColor);
-	overflow: hidden;
-	line-height: normal;
-	display: flex;
-	gap: 4px;
-	flex-direction: column;
-	box-shadow: 0 2px 2px 0px rgba(0, 0, 0, 0.1);
-	cursor: pointer;
-	border: 0;
-}
-
-.action .subheading {
-	color: var(--secondaryTextColor);
-	font-size: 0.7rem;
-}
-
-.action .desc {
-	font-size: 0.7rem;
-}
-
-.loadingContainer {
-	padding: 16px;
-	display: flex;
-	gap: 16px;
-	align-items: center;
-	justify-content: center;
-}
-
 .filesArea {
 	grid-column: 1;
 	grid-row: 2;
diff --git a/src/ui/src/components/workflows/WorkflowsWorkflow.vue b/src/ui/src/components/workflows/WorkflowsWorkflow.vue
index 103051ded..05cae3204 100644
--- a/src/ui/src/components/workflows/WorkflowsWorkflow.vue
+++ b/src/ui/src/components/workflows/WorkflowsWorkflow.vue
@@ -59,6 +59,7 @@
 				variant="secondary"
 				size="small"
 				:data-writer-unselectable="true"
+				data-automation-action="run-workflow"
 				@click="handleRun"
 			>
 				<i class="material-symbols-outlined">play_arrow</i>
diff --git a/src/ui/src/core/auditAndFix.ts b/src/ui/src/core/auditAndFix.ts
index 8760b7074..13ecd74b6 100644
--- a/src/ui/src/core/auditAndFix.ts
+++ b/src/ui/src/core/auditAndFix.ts
@@ -57,6 +57,7 @@ function auditOrphanComponents(components: ComponentMap) {
 		Object.entries(components).map(([componentId]) => [componentId, false]),
 	);
 	traverseComponentTree("root", components, visited);
+	traverseComponentTree("workflows_root", components, visited);
 	Object.entries(visited).forEach(([componentId, isVisited]) => {
 		if (!isVisited) {
 			console.warn(
diff --git a/src/writer/__init__.py b/src/writer/__init__.py
index 29fb3548e..b0ff35089 100644
--- a/src/writer/__init__.py
+++ b/src/writer/__init__.py
@@ -7,7 +7,6 @@
 from writer.core import (
     BytesWrapper,
     Config,
-    EditableDataframe,
     FileWrapper,
     Readable,
     State,
@@ -22,6 +21,7 @@
 from writer.core import (
     writerproperty as property,
 )
+from writer.core_df import EditableDataframe
 
 try:
     from writer.ui import WriterUIManager
diff --git a/src/writer/ai.py b/src/writer/ai.py
index bb260a9ad..569bb63bb 100644
--- a/src/writer/ai.py
+++ b/src/writer/ai.py
@@ -1663,10 +1663,15 @@ def _process_stream_response(
                 chunk |= {"chunk": True}
 
             # Handling tool call fragments
-            if chunk.get("tool_calls") is not None:
-                self += chunk
-                self._process_streaming_tool_calls(chunk)
-                if chunk_data.get("finish_reason") == "tool_calls":
+            tool_calls_present = chunk.get("tool_calls") is not None
+            tool_calls_need_processing = \
+                chunk_data.get("finish_reason") == "tool_calls"
+            if tool_calls_present or tool_calls_need_processing:
+                # Handle tool calls chunks
+                if tool_calls_present:
+                    self += chunk
+                    self._process_streaming_tool_calls(chunk)
+                if tool_calls_need_processing:
                     # Send follow-up call to LLM
                     self.messages += self._gather_tool_calls_results()
                     follow_up_response = cast(
@@ -1690,7 +1695,6 @@ def _process_stream_response(
                         )
                     finally:
                         follow_up_response.close()
-
             else:
                 # Handle regular message chunks
                 if chunk.get("content") is not None:
diff --git a/src/writer/app_runner.py b/src/writer/app_runner.py
index 73c91016d..616093a6e 100644
--- a/src/writer/app_runner.py
+++ b/src/writer/app_runner.py
@@ -1,7 +1,6 @@
 import asyncio
 import concurrent.futures
 import importlib.util
-import json
 import logging
 import logging.handlers
 import multiprocessing
@@ -47,6 +46,7 @@
     StateEnquiryResponsePayload,
     WriterEvent,
 )
+from writer.wf_project import WfProjectContext
 
 logging.basicConfig(level=logging.INFO, format='%(message)s')
 
@@ -580,6 +580,7 @@ class AppRunner:
     """
 
     UPDATE_CHECK_INTERVAL_SECONDS = 0.2
+    WF_PROJECT_SAVE_INTERVAL = 0.2
     MAX_WAIT_NOTIFY_SECONDS = 10
 
     def __init__(self, app_path: str, mode: str):
@@ -600,6 +601,7 @@ def __init__(self, app_path: str, mode: str):
         self.log_listener: Optional[LogListener] = None
         self.code_update_loop: Optional[asyncio.AbstractEventLoop] = None
         self.code_update_condition: Optional[asyncio.Condition] = None
+        self.wf_project_context = WfProjectContext(app_path=app_path)
 
         if mode not in ("edit", "run"):
             raise ValueError("Invalid mode.")
@@ -623,31 +625,31 @@ def _set_logger(self):
         self.log_listener = LogListener(self.log_queue)
         self.log_listener.start()
 
-    def _set_observer(self):
+    def _start_fs_observer(self):
         self.observer = PollingObserver(AppRunner.UPDATE_CHECK_INTERVAL_SECONDS)
         self.observer.schedule(FileEventHandler(self.reload_code_from_saved), path=self.app_path, recursive=True)
         self.observer.start()
 
-    def load(self) -> None:
-        def signal_handler(sig, frame):
-            self.shut_down()
-            sys.exit(0)
-
-        try:
-            signal.signal(signal.SIGINT, signal_handler)
-            signal.signal(signal.SIGTERM, signal_handler)
-        except ValueError:
-            # No need to handle signal as not main thread
-            pass
+    def _start_wf_project_process_write_files(self):
+        wf_project.start_process_write_files_async(self.wf_project_context, AppRunner.WF_PROJECT_SAVE_INTERVAL)
 
+    def load(self) -> None:
         self.run_code = self._load_persisted_script()
         self.bmc_components = self._load_persisted_components()
 
         if self.mode == "edit":
-            self._set_observer()
+            self._start_wf_project_process_write_files()
+            self._start_fs_observer()
 
         self._start_app_process()
 
+        # We have to create new processes as wf_projet_process before subscribing to signal.
+        # When a new process is create, the parent process is fork. The child would also subscribe to signal.
+        #
+        # When signal happen, both process will answer and one of them raise error due to mismatch between
+        # parent pid and pid.
+        self._subscribe_terminal_signal()
+
     async def dispatch_message(self, session_id: Optional[str], request: AppProcessServerRequest) -> AppProcessServerResponse:
 
         """
@@ -730,7 +732,7 @@ async def update_components(self, session_id: str, payload: ComponentUpdateReque
                 "Cannot update components in non-update mode.")
         self.bmc_components = payload.components
 
-        wf_project.write_files(self.app_path, metadata={"writer_version": VERSION}, components=payload.components)
+        wf_project.write_files_async(self.wf_project_context, metadata={"writer_version": VERSION}, components=payload.components)
 
         return await self.dispatch_message(session_id, ComponentUpdateRequest(
             type="componentUpdate",
@@ -796,6 +798,9 @@ def shut_down(self) -> None:
         self.log_queue.put(None)
         if self.log_listener is not None:
             self.log_listener.join()
+
+        wf_project.shutdown_process_write_files_async(self.wf_project_context)
+
         self._clean_process()
 
     def _start_app_process(self) -> None:
@@ -876,3 +881,15 @@ def run_async_in_thread():
         thread.start()
         thread.join()
         return
+
+    def _subscribe_terminal_signal(self):
+        def signal_handler(sig, frame):
+            self.shut_down()
+            sys.exit(0)
+
+        try:
+            signal.signal(signal.SIGINT, signal_handler)
+            signal.signal(signal.SIGTERM, signal_handler)
+        except ValueError:
+            # No need to handle signal as not main thread
+            pass
diff --git a/src/writer/blocks/__init__.py b/src/writer/blocks/__init__.py
new file mode 100644
index 000000000..66bfdece4
--- /dev/null
+++ b/src/writer/blocks/__init__.py
@@ -0,0 +1,33 @@
+from writer.blocks.addtostatelist import AddToStateList
+from writer.blocks.calleventhandler import CallEventHandler
+from writer.blocks.foreach import ForEach
+from writer.blocks.httprequest import HTTPRequest
+from writer.blocks.logmessage import LogMessage
+from writer.blocks.parsejson import ParseJSON
+from writer.blocks.returnvalue import ReturnValue
+from writer.blocks.runworkflow import RunWorkflow
+from writer.blocks.setstate import SetState
+from writer.blocks.writeraddchatmessage import WriterAddChatMessage
+from writer.blocks.writeraddtokg import WriterAddToKG
+from writer.blocks.writerchat import WriterChat
+from writer.blocks.writerclassification import WriterClassification
+from writer.blocks.writercompletion import WriterCompletion
+from writer.blocks.writerinitchat import WriterInitChat
+from writer.blocks.writernocodeapp import WriterNoCodeApp
+
+SetState.register("workflows_setstate")
+WriterClassification.register("workflows_writerclassification")
+WriterCompletion.register("workflows_writercompletion")
+HTTPRequest.register("workflows_httprequest")
+RunWorkflow.register("workflows_runworkflow")
+WriterNoCodeApp.register("workflows_writernocodeapp")
+ForEach.register("workflows_foreach")
+LogMessage.register("workflows_logmessage")
+WriterChat.register("workflows_writerchat")
+WriterAddChatMessage.register("workflows_writeraddchatmessage")
+ParseJSON.register("workflows_parsejson")
+CallEventHandler.register("workflows_calleventhandler")
+AddToStateList.register("workflows_addtostatelist")
+ReturnValue.register("workflows_returnvalue")
+WriterInitChat.register("workflows_writerinitchat")
+WriterAddToKG.register("workflows_writeraddtokg")
diff --git a/src/writer/workflows_blocks/addtostatelist.py b/src/writer/blocks/addtostatelist.py
similarity index 83%
rename from src/writer/workflows_blocks/addtostatelist.py
rename to src/writer/blocks/addtostatelist.py
index f2b3e0f97..26be22f78 100644
--- a/src/writer/workflows_blocks/addtostatelist.py
+++ b/src/writer/blocks/addtostatelist.py
@@ -1,6 +1,6 @@
 from writer.abstract import register_abstract_template
-from writer.ss_types import AbstractTemplate
-from writer.workflows_blocks.blocks import WorkflowBlock
+from writer.blocks.base_block import WorkflowBlock
+from writer.ss_types import AbstractTemplate, WriterConfigurationError
 
 
 class AddToStateList(WorkflowBlock):
@@ -45,15 +45,15 @@ def run(self):
             element_expr = self._get_field("element")
             value = self._get_field("value")
 
-            element = self.evaluator.evaluate_expression(element_expr, self.instance_path, self.execution_env)
+            element = self.evaluator.evaluate_expression(element_expr, self.instance_path, self.execution_environment)
 
             if not element:
                 element = []
             elif not isinstance(element, list):
-                element = [element]
+                raise WriterConfigurationError(f'The state element must be a list. A value of type "{type(element)}" was found.')
 
             element.append(value)
-            self.evaluator.set_state(element_expr, self.instance_path, element, base_context=self.execution_env)
+            self._set_state(element_expr, element)
             self.outcome = "success"
         except BaseException as e:
             self.outcome = "error"
diff --git a/src/writer/blocks/base_block.py b/src/writer/blocks/base_block.py
new file mode 100644
index 000000000..6d064a912
--- /dev/null
+++ b/src/writer/blocks/base_block.py
@@ -0,0 +1,58 @@
+from typing import TYPE_CHECKING, Any, Dict, Type
+
+import writer.evaluator
+from writer.ss_types import WriterConfigurationError
+
+if TYPE_CHECKING:
+    from writer.core_ui import Component
+    from writer.ss_types import InstancePath
+    from writer.workflows import WorkflowRunner
+
+WorkflowBlock_T = Type["WorkflowBlock"]
+block_map:Dict[str, WorkflowBlock_T] = {}
+
+class WorkflowBlock:
+    
+    @classmethod
+    def register(cls, type: str):
+        block_map[type] = cls
+
+    def __init__(self, component_id: str, runner: "WorkflowRunner", execution_environment: Dict):
+        self.outcome = None
+        self.message = None
+        self.component_id = component_id
+        self.runner = runner
+        self.execution_time_in_seconds = -1.0
+        self.execution_environment = execution_environment
+        self.result = None
+        self.return_value = None
+        self.instance_path: InstancePath = [{"componentId": component_id, "instanceNumber": 0}]
+        self.evaluator = writer.evaluator.Evaluator(runner.session.session_state, runner.session.session_component_tree)
+
+    def _handle_missing_field(self, field_key):
+        component_tree = self.runner.session.session_component_tree
+        component = component_tree.get_component(self.component_id)
+        field_content = component.content.get(field_key)
+        if field_content:
+            raise WriterConfigurationError(f'The field `{field_key}` is required. The expression specified, `{field_content}`, resulted in an empty value.')
+        else:
+            raise WriterConfigurationError(f'The field `{field_key}` is required. It was left empty.')
+
+    def _get_field(self, field_key: str, as_json=False, default_field_value=None, required=False):
+        if default_field_value is None:
+            if as_json:
+                default_field_value = "{}"
+            else:
+                default_field_value = ""
+        value = self.evaluator.evaluate_field(self.instance_path, field_key, as_json, default_field_value, self.execution_environment)
+
+        if required and (value is None or value == "" or value == {}):
+            self._handle_missing_field(field_key)
+            
+        return value
+
+    def _set_state(self, expr: str, value: Any):
+        self.evaluator.set_state(expr, self.instance_path, value, base_context=self.execution_environment)
+
+    def run(self):
+        pass
\ No newline at end of file
diff --git a/src/writer/workflows_blocks/calleventhandler.py b/src/writer/blocks/calleventhandler.py
similarity index 93%
rename from src/writer/workflows_blocks/calleventhandler.py
rename to src/writer/blocks/calleventhandler.py
index 62798494f..31d08d9dc 100644
--- a/src/writer/workflows_blocks/calleventhandler.py
+++ b/src/writer/blocks/calleventhandler.py
@@ -1,10 +1,9 @@
 import inspect
 
 import writer.core
-import writer.workflows
 from writer.abstract import register_abstract_template
+from writer.blocks.base_block import WorkflowBlock
 from writer.ss_types import AbstractTemplate
-from writer.workflows_blocks.blocks import WorkflowBlock
 
 
 class CallEventHandler(WorkflowBlock):
@@ -57,8 +56,8 @@ def run(self):
             callable_handler = handler_registry.find_handler_callable(handler_name)
 
             args = {
-                "state": self.session.session_state,
-                "context": self.execution_env,
+                "state": self.runner.session.session_state,
+                "context": self.execution_environment,
                 "session": writer.core._event_handler_session_info(),
             } | additional_args
 
diff --git a/src/writer/workflows_blocks/foreach.py b/src/writer/blocks/foreach.py
similarity index 84%
rename from src/writer/workflows_blocks/foreach.py
rename to src/writer/blocks/foreach.py
index 183064abf..b5268d625 100644
--- a/src/writer/workflows_blocks/foreach.py
+++ b/src/writer/blocks/foreach.py
@@ -1,7 +1,6 @@
-import writer.workflows
 from writer.abstract import register_abstract_template
+from writer.blocks.base_block import WorkflowBlock
 from writer.ss_types import AbstractTemplate
-from writer.workflows_blocks.blocks import WorkflowBlock
 
 
 class ForEach(WorkflowBlock):
@@ -52,22 +51,23 @@ def register(cls, type: str):
             }
         ))
 
-    def _run_workflow_for_item(self, workflow_key, base_execution_env, item_id, item):
-        return writer.workflows.run_workflow_by_key(self.session, workflow_key, base_execution_env | { "itemId": item_id, "item": item })
+    def _run_workflow_for_item(self, workflow_key, base_execution_environment, item_id, item):
+        expanded_execution_environment = base_execution_environment | { "itemId": item_id, "item": item }
+        return self.runner.run_workflow_by_key(workflow_key, expanded_execution_environment)
 
     def run(self):
         try:
             workflow_key = self._get_field("workflowKey")
             items = self._get_field("items", as_json=True)
-            base_execution_env = self._get_field("executionEnv", as_json=True)
+            base_execution_environment = self._get_field("executionEnv", as_json=True)
             std_items = items
             result = None
             if isinstance(items, list):
                 std_items = enumerate(std_items, 0)
-                result = [self._run_workflow_for_item(workflow_key, base_execution_env, item_id, item) for item_id, item in std_items]
+                result = [self._run_workflow_for_item(workflow_key, base_execution_environment, item_id, item) for item_id, item in std_items]
             elif isinstance(items, dict):
                 std_items = items.items()
-                result = {item_id:self._run_workflow_for_item(workflow_key, base_execution_env, item_id, item) for item_id, item in std_items}
+                result = {item_id:self._run_workflow_for_item(workflow_key, base_execution_environment, item_id, item) for item_id, item in std_items}
 
             self.result = result
             self.outcome = "success"
diff --git a/src/writer/workflows_blocks/httprequest.py b/src/writer/blocks/httprequest.py
similarity index 92%
rename from src/writer/workflows_blocks/httprequest.py
rename to src/writer/blocks/httprequest.py
index aa77f4977..6d403734c 100644
--- a/src/writer/workflows_blocks/httprequest.py
+++ b/src/writer/blocks/httprequest.py
@@ -1,8 +1,8 @@
 import requests
 
 from writer.abstract import register_abstract_template
+from writer.blocks.base_block import WorkflowBlock
 from writer.ss_types import AbstractTemplate
-from writer.workflows_blocks.blocks import WorkflowBlock
 
 
 class HTTPRequest(WorkflowBlock):
@@ -68,7 +68,7 @@ def run(self):
         import json
 
         try:
-            method = self._get_field("method", False, "get")
+            method = self._get_field("method", False, "GET")
             url = self._get_field("url")
             headers = self._get_field("headers", True)
             body = self._get_field("body")
@@ -87,9 +87,10 @@ def run(self):
             else:
                 self.outcome = "responseError"
                 raise RuntimeError("HTTP response with code " + str(req.status_code))
-        except json.JSONDecodeError:
-            self.result = "JSON decode error. The response contains invalid JSON."
+        except json.JSONDecodeError as e:
             self.outcome = "responseError"
+            raise e
         except BaseException as e:
-            self.outcome = "connectionError"
+            if not self.outcome:
+                self.outcome = "connectionError"
             raise e
\ No newline at end of file
diff --git a/src/writer/workflows_blocks/logmessage.py b/src/writer/blocks/logmessage.py
similarity index 83%
rename from src/writer/workflows_blocks/logmessage.py
rename to src/writer/blocks/logmessage.py
index 2cba940e5..c2013172c 100644
--- a/src/writer/workflows_blocks/logmessage.py
+++ b/src/writer/blocks/logmessage.py
@@ -1,7 +1,6 @@
-import writer.workflows
 from writer.abstract import register_abstract_template
+from writer.blocks.base_block import WorkflowBlock
 from writer.ss_types import AbstractTemplate
-from writer.workflows_blocks.blocks import WorkflowBlock
 
 
 class LogMessage(WorkflowBlock):
@@ -49,13 +48,9 @@ def register(cls, type: str):
     def run(self):
         try:
             type = self._get_field("type", False, "info")
-            message = self._get_field("message")
+            message = self._get_field("message", required=True)
 
-            if message is None:
-                self.result = "Message cannot be empty."
-                self.outcome = "error"
-
-            self.session.session_state.add_log_entry(type, "Workflows message", message)
+            self.runner.session.session_state.add_log_entry(type, "Workflows message", message)
             self.result = None
             self.outcome = "success"
         except BaseException as e:
diff --git a/src/writer/workflows_blocks/parsejson.py b/src/writer/blocks/parsejson.py
similarity index 96%
rename from src/writer/workflows_blocks/parsejson.py
rename to src/writer/blocks/parsejson.py
index 784d1427a..da6576df8 100644
--- a/src/writer/workflows_blocks/parsejson.py
+++ b/src/writer/blocks/parsejson.py
@@ -1,8 +1,8 @@
 import json
 
 from writer.abstract import register_abstract_template
+from writer.blocks.base_block import WorkflowBlock
 from writer.ss_types import AbstractTemplate
-from writer.workflows_blocks.blocks import WorkflowBlock
 
 
 class ParseJSON(WorkflowBlock):
diff --git a/src/writer/workflows_blocks/returnvalue.py b/src/writer/blocks/returnvalue.py
similarity index 87%
rename from src/writer/workflows_blocks/returnvalue.py
rename to src/writer/blocks/returnvalue.py
index 6770565cd..b54cb2bf1 100644
--- a/src/writer/workflows_blocks/returnvalue.py
+++ b/src/writer/blocks/returnvalue.py
@@ -1,7 +1,6 @@
-import writer.workflows
 from writer.abstract import register_abstract_template
-from writer.ss_types import AbstractTemplate
-from writer.workflows_blocks.blocks import WorkflowBlock
+from writer.blocks.base_block import WorkflowBlock
+from writer.ss_types import AbstractTemplate, WriterConfigurationError
 
 
 class ReturnValue(WorkflowBlock):
@@ -41,7 +40,7 @@ def run(self):
         try:
             value = self._get_field("value")
             if value is None:
-                raise ValueError("Return value cannot be empty or None.")
+                raise WriterConfigurationError("Return value cannot be empty or None.")
             self.result = value
             self.return_value = value
             self.outcome = "success"
diff --git a/src/writer/workflows_blocks/runworkflow.py b/src/writer/blocks/runworkflow.py
similarity index 87%
rename from src/writer/workflows_blocks/runworkflow.py
rename to src/writer/blocks/runworkflow.py
index 247e2c236..e9042cc42 100644
--- a/src/writer/workflows_blocks/runworkflow.py
+++ b/src/writer/blocks/runworkflow.py
@@ -1,7 +1,6 @@
-import writer.workflows
 from writer.abstract import register_abstract_template
+from writer.blocks.base_block import WorkflowBlock
 from writer.ss_types import AbstractTemplate
-from writer.workflows_blocks.blocks import WorkflowBlock
 
 
 class RunWorkflow(WorkflowBlock):
@@ -46,9 +45,9 @@ def register(cls, type: str):
     def run(self):
         try:
             workflow_key = self._get_field("workflowKey")
-            execution_env = self._get_field("executionEnv", as_json=True)
+            execution_environment = self._get_field("executionEnv", as_json=True)
 
-            return_value = writer.workflows.run_workflow_by_key(self.session, workflow_key, execution_env)
+            return_value = self.runner.run_workflow_by_key(workflow_key, execution_environment)
             self.result = return_value
             self.outcome = "success"
         except BaseException as e:
diff --git a/src/writer/workflows_blocks/setstate.py b/src/writer/blocks/setstate.py
similarity index 88%
rename from src/writer/workflows_blocks/setstate.py
rename to src/writer/blocks/setstate.py
index 389c8a224..0249df136 100644
--- a/src/writer/workflows_blocks/setstate.py
+++ b/src/writer/blocks/setstate.py
@@ -1,6 +1,6 @@
 from writer.abstract import register_abstract_template
+from writer.blocks.base_block import WorkflowBlock
 from writer.ss_types import AbstractTemplate
-from writer.workflows_blocks.blocks import WorkflowBlock
 
 
 class SetState(WorkflowBlock):
@@ -42,9 +42,10 @@ def register(cls, type: str):
 
     def run(self):
         try:
-            element = self._get_field("element")
+            element = self._get_field("element", required=True)
             value = self._get_field("value")
-            self.evaluator.set_state(element, self.instance_path, value, base_context=self.execution_env)
+
+            self._set_state(element, value)
             self.result = value
             self.outcome = "success"
         except BaseException as e:
diff --git a/src/writer/workflows_blocks/writeraddchatmessage.py b/src/writer/blocks/writeraddchatmessage.py
similarity index 66%
rename from src/writer/workflows_blocks/writeraddchatmessage.py
rename to src/writer/blocks/writeraddchatmessage.py
index 1d9a9f235..e4d8ebe24 100644
--- a/src/writer/workflows_blocks/writeraddchatmessage.py
+++ b/src/writer/blocks/writeraddchatmessage.py
@@ -1,6 +1,6 @@
 from writer.abstract import register_abstract_template
-from writer.ss_types import AbstractTemplate
-from writer.workflows_blocks.blocks import WorkflowBlock
+from writer.blocks.base_block import WorkflowBlock
+from writer.ss_types import AbstractTemplate, WriterConfigurationError
 
 
 class WriterAddChatMessage(WorkflowBlock):
@@ -45,33 +45,19 @@ def run(self):
         try:
             import writer.ai
 
-            conversation_state_element = self._get_field("conversationStateElement")
-            message = self._get_field("message", as_json=True)
-            conversation = self.evaluator.evaluate_expression(conversation_state_element, self.instance_path, self.execution_env)
+            conversation_state_element = self._get_field("conversationStateElement", required=True)
+            message = self._get_field("message", as_json=True, required=True)
 
-            if conversation is None or not isinstance(conversation, writer.ai.Conversation):
-                self.result = "The state element specified doesn't contain a conversation. Initialize one using the block 'Initialize chat'."
-                self.outcome = "error"
-                return
+            conversation = self.evaluator.evaluate_expression(conversation_state_element, self.instance_path, self.execution_environment)
 
-            if message is None:
-                self.result = "No message has been specified."
-                self.outcome = "error"
-                return
+            if conversation is None or not isinstance(conversation, writer.ai.Conversation):
+                raise WriterConfigurationError("The state element specified doesn't contain a conversation. Initialize one using the block 'Initialize chat'.")
             
-            try:
-                writer.ai.Conversation.validate_message(message)
-            except ValueError:
-                self.result = "Invalid message."
-                self.outcome = "error"
-            finally:
-                if self.outcome:
-                    return            
-
+            writer.ai.Conversation.validate_message(message)
             conversation += message
 
-            self.evaluator.set_state(conversation_state_element, self.instance_path, conversation, base_context=self.execution_env)            
-            self.result = "Success"
+            self._set_state(conversation_state_element, conversation)            
+            self.result = None
             self.outcome = "success"
         except BaseException as e:
             self.outcome = "error"
diff --git a/src/writer/blocks/writeraddtokg.py b/src/writer/blocks/writeraddtokg.py
new file mode 100644
index 000000000..dcaa415f0
--- /dev/null
+++ b/src/writer/blocks/writeraddtokg.py
@@ -0,0 +1,81 @@
+from typing import Any
+
+from writer.abstract import register_abstract_template
+from writer.blocks.base_block import WorkflowBlock
+from writer.ss_types import AbstractTemplate, WriterConfigurationError
+
+
+class WriterAddToKG(WorkflowBlock):
+
+    @classmethod
+    def register(cls, type: str):
+        super(WriterAddToKG, cls).register(type)
+        register_abstract_template(type, AbstractTemplate(
+            baseType="workflows_node",
+            writer={
+                "name": "Add to Knowledge Graph",
+                "description": "Adds files to an existing knowledge graph.",
+                "category": "Writer",
+                "fields": {
+                    "graphId": {
+                        "name": "Graph id",
+                        "type": "Text",
+                        "desc": "The id for an existing knowledge graph. It has a UUID format."
+                    },
+                    "files": {
+                        "name": "Files",
+                        "type": "Object",
+                        "default": "[]",
+                        "desc": "A list of files to be uploaded and added to the knowledge graph. You can use files uploaded via the File Input component or specify dictionaries with data, type and name."
+                    },
+                },
+                "outs": {
+                    "success": {
+                        "name": "Success",
+                        "description": "If the execution was successful.",
+                        "style": "success",
+                    },
+                    "error": {
+                        "name": "Error",
+                        "description": "If the function raises an Exception.",
+                        "style": "error",
+                    },
+                },
+            }
+        ))
+
+    def _get_prepared_file(self, raw_file: Any):
+        if not isinstance(raw_file, dict):
+            raise WriterConfigurationError("Files must be dictionaries and contain `data`, `type` and `name` attributes.")
+
+        if "data" not in raw_file or "type" not in raw_file or "name" not in raw_file:
+            raise WriterConfigurationError("A file specified as a dictionary must contain `data`, `type` and `name` attributes.")
+
+        return raw_file
+
+    def run(self):
+        try:
+            import writer.ai
+
+            graph_id = self._get_field("graphId", required=True)
+            raw_files = self._get_field("files", as_json=True)
+            prepared_files = []
+
+            if not isinstance(raw_files, list):
+                raise WriterConfigurationError("Files must be a list.")
+
+            for raw_file in raw_files:
+                prepared_files.append(self._get_prepared_file(raw_file))
+                
+            graph = writer.ai.retrieve_graph(graph_id)
+            
+            for prepared_file in prepared_files:
+                file = writer.ai.upload_file(prepared_file.get("data"),
+                                             prepared_file.get("type"),
+                                             prepared_file.get("name"))
+                graph.add_file(file)
+
+            self.outcome = "success"
+        except BaseException as e:
+            self.outcome = "error"
+            raise e
\ No newline at end of file
diff --git a/src/writer/workflows_blocks/writerchat.py b/src/writer/blocks/writerchat.py
similarity index 60%
rename from src/writer/workflows_blocks/writerchat.py
rename to src/writer/blocks/writerchat.py
index 02afe9558..4a3f73f7a 100644
--- a/src/writer/workflows_blocks/writerchat.py
+++ b/src/writer/blocks/writerchat.py
@@ -1,7 +1,6 @@
-import writer.workflows
 from writer.abstract import register_abstract_template
+from writer.blocks.base_block import WorkflowBlock
 from writer.ss_types import AbstractTemplate
-from writer.workflows_blocks.blocks import WorkflowBlock
 
 
 class WriterChat(WorkflowBlock):
@@ -58,35 +57,23 @@ def register(cls, type: str):
             }
         ))
 
-    def run_branch(self, outcome: str, **args):
-        branch_root_nodes = self._get_nodes_at_outcome(outcome)
-        return_value = None
-        for branch_root_node in branch_root_nodes:
-            branch_nodes = writer.workflows.get_branch_nodes(branch_root_node.id)
-            terminal_nodes = writer.workflows.get_terminal_nodes(branch_nodes)
-
-            for terminal_node in terminal_nodes:
-                tool = writer.workflows.run_node(terminal_node, branch_nodes, self.execution, self.session, self.execution_env | args)
-                if tool and tool.return_value:
-                    return_value = tool.return_value
-
-        if return_value is None:
-            self.result = f"No value has been returned for the outcome branch '{outcome}'. Use the block 'Return value' to specify one."
-            self.outcome = "error"
-            raise ValueError("No value available")
-
-        return repr(return_value)
-
     def _make_callable(self, tool_name: str):
         def callable(**args):
-            return self.run_branch(f"tools_{tool_name}", **args)
+            expanded_execution_environment = self.execution_environment | args
+            return_value = self.runner.run_branch(self.component_id, f"tools_{tool_name}", expanded_execution_environment, f"Workflow branch execution (chat tool {tool_name})")
+
+            if return_value is None:
+                self.outcome = "error"
+                raise ValueError(f'No value has been returned for the outcome branch "{tool_name}". Use the block "Return value" to specify one.')
+
+            return return_value
         return callable
 
     def run(self):
         try:
             import writer.ai
 
-            conversation_state_element = self._get_field("conversationStateElement")
+            conversation_state_element = self._get_field("conversationStateElement", required=True)
             use_streaming = self._get_field("useStreaming", False, "yes") == "yes"
             tools_raw = self._get_field("tools", True)
             tools = []
@@ -111,37 +98,26 @@ def run(self):
                     continue
                 tools.append(tool)
 
-            conversation = self.evaluator.evaluate_expression(conversation_state_element, self.instance_path, self.execution_env)
+            conversation = self.evaluator.evaluate_expression(conversation_state_element, self.instance_path, self.execution_environment)
 
             if conversation is None or not isinstance(conversation, writer.ai.Conversation):
-                self.result = "The state element specified doesn't contain a conversation. Initialize one using the block 'Initialize chat'."
-                self.outcome = "error"
-                return
+                raise ValueError("The state element specified doesn't contain a conversation. Initialize one using the block 'Initialize chat'.")
 
-            try:
-                msg = ""
-                if not use_streaming:
-                    msg = conversation.complete(tools=tools)
-                    conversation += msg
-                    self.evaluator.set_state(conversation_state_element, self.instance_path, conversation, base_context=self.execution_env)
-                else:
-                    for chunk in conversation.stream_complete(tools=tools):
-                        if chunk.get("content") is None:
-                            chunk["content"] = ""
-                        msg += chunk.get("content")
-                        conversation += chunk
-                        self.evaluator.set_state(conversation_state_element, self.instance_path, conversation, base_context=self.execution_env)
-            except BaseException:
-                msg = {
-                    "role": "assistant",
-                    "content": "Couldn't process the request."
-                }
+            msg = ""
+            if not use_streaming:
+                msg = conversation.complete(tools=tools)
                 conversation += msg
-                self.evaluator.set_state(conversation_state_element, self.instance_path, conversation, base_context=self.execution_env)
+                self._set_state(conversation_state_element, conversation)
+            else:
+                for chunk in conversation.stream_complete(tools=tools):
+                    if chunk.get("content") is None:
+                        chunk["content"] = ""
+                    msg += chunk.get("content")
+                    conversation += chunk
+                    self._set_state(conversation_state_element, conversation)
             
-            if not self.outcome:
-                self.result = msg
-                self.outcome = "success"
+            self.result = msg
+            self.outcome = "success"
         except BaseException as e:
             self.outcome = "error"
             raise e
\ No newline at end of file
diff --git a/src/writer/workflows_blocks/writerclassification.py b/src/writer/blocks/writerclassification.py
similarity index 85%
rename from src/writer/workflows_blocks/writerclassification.py
rename to src/writer/blocks/writerclassification.py
index b9f9f7826..690159ac8 100644
--- a/src/writer/workflows_blocks/writerclassification.py
+++ b/src/writer/blocks/writerclassification.py
@@ -1,8 +1,8 @@
 import json
 
 from writer.abstract import register_abstract_template
+from writer.blocks.base_block import WorkflowBlock
 from writer.ss_types import AbstractTemplate
-from writer.workflows_blocks.blocks import WorkflowBlock
 
 
 class WriterClassification(WorkflowBlock):
@@ -33,8 +33,9 @@ def register(cls, type: str):
                     },
                 },
                 "outs": {
-                    "$dynamic": {
-                        "field": "categories"
+                    "category": {
+                        "field": "categories",
+                        "style": "dynamic"
                     },
                     "error": {
                         "name": "Error",
@@ -49,14 +50,11 @@ def run(self):
         try:
             import writer.ai
 
-            text = self._get_field("text")
+            text = self._get_field("text", required=True)
             additional_context = self._get_field("additionalContext")
-            categories = self._get_field("categories", as_json=True)
-            # model_id = self._get_field("modelId")
+            categories = self._get_field("categories", as_json=True, required=True)
 
             config = {}
-            # if model_id:
-            #     config["model"] = model_id
 
             prompt = f"""
 Classify the text under “CONTENT” into one of the following categories:
@@ -75,7 +73,7 @@ def run(self):
 """
             result = writer.ai.complete(prompt, config).strip()
             self.result = result
-            self.outcome = f"$dynamic_{result}"
+            self.outcome = f"category_{result}"
         except BaseException as e:
             self.outcome = "error"
             raise e
\ No newline at end of file
diff --git a/src/writer/workflows_blocks/writercompletion.py b/src/writer/blocks/writercompletion.py
similarity index 97%
rename from src/writer/workflows_blocks/writercompletion.py
rename to src/writer/blocks/writercompletion.py
index 213dc7eb7..d1980397d 100644
--- a/src/writer/workflows_blocks/writercompletion.py
+++ b/src/writer/blocks/writercompletion.py
@@ -1,6 +1,6 @@
 from writer.abstract import register_abstract_template
+from writer.blocks.base_block import WorkflowBlock
 from writer.ss_types import AbstractTemplate
-from writer.workflows_blocks.blocks import WorkflowBlock
 
 DEFAULT_MODEL = "palmyra-x-003-instruct"
 
diff --git a/src/writer/workflows_blocks/writerinitchat.py b/src/writer/blocks/writerinitchat.py
similarity index 83%
rename from src/writer/workflows_blocks/writerinitchat.py
rename to src/writer/blocks/writerinitchat.py
index 68c52a8ff..de560420d 100644
--- a/src/writer/workflows_blocks/writerinitchat.py
+++ b/src/writer/blocks/writerinitchat.py
@@ -1,6 +1,6 @@
 from writer.abstract import register_abstract_template
-from writer.ss_types import AbstractTemplate
-from writer.workflows_blocks.blocks import WorkflowBlock
+from writer.blocks.base_block import WorkflowBlock
+from writer.ss_types import AbstractTemplate, WriterConfigurationError
 
 DEFAULT_MODEL = "palmyra-x-004"
 
@@ -14,7 +14,7 @@ def register(cls, type: str):
             baseType="workflows_node",
             writer={
                 "name": "Initialize chat",
-                "description": "If it doesn't already exist, initializes a conversation for Chat Completion",
+                "description": "If it doesn't already exist, initializes a conversation for Chat completion",
                 "category": "Writer",
                 "fields": {
                     "conversationStateElement": {
@@ -57,19 +57,17 @@ def run(self):
             model_id = self._get_field("modelId", False, default_field_value=DEFAULT_MODEL)
             config = { "temperature": temperature, "model": model_id}
 
-            conversation = self.evaluator.evaluate_expression(conversation_state_element, self.instance_path, self.execution_env)
+            conversation = self.evaluator.evaluate_expression(conversation_state_element, self.instance_path, self.execution_environment)
 
             if conversation is not None and not isinstance(conversation, writer.ai.Conversation):
-                self.result = f"The state element specified doesn't contain a Conversation. A value of type {type(conversation)} was found."
-                self.outcome = "error"
-                return
+                raise WriterConfigurationError(f'The state element specified does not contain a Conversation. A value of type "{type(conversation)}" was found.')
             elif conversation is not None:
-                self.result = "The conversation already exists."
+                self.result = "The conversation already exists. It will not be overwritten."
                 self.outcome = "success"
                 return
 
             conversation = writer.ai.Conversation(config=config)
-            self.evaluator.set_state(conversation_state_element, self.instance_path, conversation, base_context=self.execution_env)
+            self._set_state(conversation_state_element, conversation)
             self.result = None
             self.outcome = "success"
         except BaseException as e:
diff --git a/src/writer/workflows_blocks/writernocodeapp.py b/src/writer/blocks/writernocodeapp.py
similarity index 94%
rename from src/writer/workflows_blocks/writernocodeapp.py
rename to src/writer/blocks/writernocodeapp.py
index 8fb55a0b9..1f505739d 100644
--- a/src/writer/workflows_blocks/writernocodeapp.py
+++ b/src/writer/blocks/writernocodeapp.py
@@ -1,8 +1,6 @@
-import json
-
 from writer.abstract import register_abstract_template
+from writer.blocks.base_block import WorkflowBlock
 from writer.ss_types import AbstractTemplate
-from writer.workflows_blocks.blocks import WorkflowBlock
 
 
 class WriterNoCodeApp(WorkflowBlock):
@@ -47,7 +45,7 @@ def run(self):
         try:
             import writer.ai
 
-            application_id = self._get_field("appId")
+            application_id = self._get_field("appId", required=True)
             app_inputs = self._get_field("appInputs", as_json=True)
 
             # config = {}
diff --git a/src/writer/core.py b/src/writer/core.py
index d3e8c9e6f..72c03c3c7 100644
--- a/src/writer/core.py
+++ b/src/writer/core.py
@@ -7,18 +7,15 @@
 import functools
 import inspect
 import io
-import json
 import logging
 import math
 import multiprocessing
 import numbers
-import os
 import re
 import secrets
 import time
 import traceback
 import urllib.request
-from abc import ABCMeta
 from contextvars import ContextVar
 from multiprocessing.process import BaseProcess
 from types import ModuleType
@@ -44,15 +41,12 @@
 
 import pyarrow  # type: ignore
 
-import writer.workflows
+import writer.blocks
+import writer.evaluator
 from writer import core_ui
 from writer.core_ui import Component
 from writer.ss_types import (
-    DataframeRecordAdded,
-    DataframeRecordRemoved,
-    DataframeRecordUpdated,
     InstancePath,
-    InstancePathItem,
     Readable,
     ServeMode,
     WorkflowExecutionLog,
@@ -63,7 +57,6 @@
 
 if TYPE_CHECKING:
     import pandas
-    import polars
 
     from writer.app_runner import AppProcess
     from writer.ss_types import AppProcessServerRequest
@@ -137,6 +130,29 @@ class Config:
     logger: Optional[logging.Logger] = None
     feature_flags: list[str] = []
 
+
+class WriterSession:
+
+    """
+    Represents a session.
+    """
+
+    def __init__(self, session_id: str, cookies: Optional[Dict[str, str]], headers: Optional[Dict[str, str]]) -> None:
+        self.session_id = session_id
+        self.cookies = cookies
+        self.headers = headers
+        self.last_active_timestamp: int = int(time.time())
+        new_state = WriterState.get_new()
+        new_state.user_state.mutated = set()
+        self.session_state = new_state
+        self.session_component_tree = core_ui.build_session_component_tree(base_component_tree)
+        self.event_handler = EventHandler(self)
+        self.userinfo: Optional[dict] = None
+
+    def update_last_active_timestamp(self) -> None:
+        self.last_active_timestamp = int(time.time())
+
+
 @dataclasses.dataclass
 class MutationSubscription:
     """
@@ -264,6 +280,8 @@ class StateSerialiser:
     """
     def serialise(self, v: Any) -> Union[Dict, List, str, bool, int, float, None]:
         from writer.ai import Conversation
+        from writer.core_df import EditableDataframe
+
         if isinstance(v, State):
             return self._serialise_dict_recursively(v.to_dict())
         if isinstance(v, Conversation):
@@ -464,7 +482,7 @@ def __setitem__(self, key: str, raw_value: Any) -> None:
                             "new_value": raw_value
                         }
 
-                        writer_event_handler_invoke(local_mutation.handler, {
+                        EventHandlerExecutor.invoke(local_mutation.handler, {
                             "state": local_mutation.state,
                             "context": context_data,
                             "payload": payload,
@@ -834,7 +852,7 @@ def subscribe_mutation(self,
                     # existing states. To cause this, we trigger manually
                     # the handler.
                     if initial_triggered is True:
-                        writer_event_handler_invoke(handler, {
+                        EventHandlerExecutor.invoke(handler, {
                             "state": self,
                             "context": {"event": "init"},
                             "payload": {},
@@ -1083,7 +1101,7 @@ def __init__(self, middleware: Callable):
 
     @contextlib.contextmanager
     def execute(self, args: dict):
-        middleware_args = writer_event_handler_build_arguments(self.middleware, args)
+        middleware_args = EventHandlerExecutor.build_arguments(self.middleware, args)
         it = self.middleware(*middleware_args)
         try:
             yield from it
@@ -1203,8 +1221,8 @@ class EventDeserialiser:
     Its main goal is to deserialise incoming content in a controlled and predictable way,
     applying sanitisation of inputs where relevant."""
 
-    def __init__(self, session_state: WriterState, session_component_tree: core_ui.ComponentTree):
-        self.evaluator = Evaluator(session_state, session_component_tree)
+    def __init__(self, session: "WriterSession"):
+        self.evaluator = writer.evaluator.Evaluator(session.session_state, session.session_component_tree)
 
     def transform(self, ev: WriterEvent) -> None:
         # Events without payloads are safe
@@ -1448,220 +1466,6 @@ def _transform_dataframe_action(self, ev: WriterEvent) -> Optional[Dict]:
         return payload
 
 
-class Evaluator:
-
-    """
-    Evaluates templates and expressions in the backend.
-    It allows for the sanitisation of frontend inputs.
-    """
-
-    template_regex = re.compile(r"[\\]?@{([^{]*?)}")
-
-    def __init__(self, session_state: WriterState, session_component_tree: core_ui.ComponentTree):
-        self.wf = session_state
-        self.ct = session_component_tree
-
-    def evaluate_field(self, instance_path: InstancePath, field_key: str, as_json=False, default_field_value="", base_context={}) -> Any:
-        def replacer(matched):
-            if matched.string[0] == "\\":  # Escaped @, don't evaluate
-                return matched.string
-            expr = matched.group(1).strip()
-            expr_value = self.evaluate_expression(expr, instance_path, base_context)
-
-            try:
-                if as_json:
-                    serialised_value = state_serialiser.serialise(expr_value)
-                    if not isinstance(serialised_value, str):
-                        serialised_value = json.dumps(serialised_value)
-                    return serialised_value
-                return expr_value
-            except BaseException:
-                raise ValueError(
-                    f"""Couldn't serialise value of type "{ type(expr_value) }" when evaluating field "{ field_key }".""")
-
-        component_id = instance_path[-1]["componentId"]
-        component = self.ct.get_component(component_id)
-        if component:
-            field_value = component.content.get(field_key) or default_field_value
-            replaced = None
-            full_match = self.template_regex.fullmatch(field_value)
-
-            if full_match is None:
-                replaced = self.template_regex.sub(lambda m: str(replacer(m)), field_value)
-            else:
-                replaced = replacer(full_match)
-
-            if (replaced is not None) and as_json:
-                replaced_as_json = None
-                try:
-                    replaced_as_json = json.loads(replaced)
-                except json.JSONDecodeError:
-                    replaced_as_json = json.loads(default_field_value)
-                return replaced_as_json
-            else:
-                return replaced
-        else:
-            raise ValueError(f"Couldn't acquire a component by ID '{component_id}'")
-
-
-    def get_context_data(self, instance_path: InstancePath, base_context={}) -> Dict[str, Any]:
-        context: Dict[str, Any] = base_context
-        for i in range(len(instance_path)):
-            path_item = instance_path[i]
-            component_id = path_item["componentId"]
-            component = self.ct.get_component(component_id)
-            if not component:
-                continue
-            if component.type != "repeater":
-                continue
-            if i + 1 >= len(instance_path):
-                continue
-            repeater_instance_path = instance_path[0:i+1]
-            next_instance_path = instance_path[0:i+2]
-            instance_number = next_instance_path[-1]["instanceNumber"]
-            repeater_object = self.evaluate_field(
-                repeater_instance_path, "repeaterObject", True, """{ "a": { "desc": "Option A" }, "b": { "desc": "Option B" } }""")
-            key_variable = self.evaluate_field(
-                repeater_instance_path, "keyVariable", False, "itemId")
-            value_variable = self.evaluate_field(
-                repeater_instance_path, "valueVariable", False, "item")
-
-            repeater_items: List[Tuple[Any, Any]] = []
-            if isinstance(repeater_object, dict):
-                repeater_items = list(repeater_object.items())
-            elif isinstance(repeater_object, list):
-                repeater_items = list(enumerate(repeater_object))
-            else:
-                raise ValueError(
-                    "Cannot produce context. Repeater object must evaluate to a dictionary.")
-
-            context[key_variable] = repeater_items[instance_number][0]
-            context[value_variable] = repeater_items[instance_number][1]
-
-        if len(instance_path) > 0:
-            context['target'] = instance_path[-1]['componentId']
-
-        return context
-
-    def set_state(self, expr: str, instance_path: InstancePath, value: Any, base_context = {}) -> None:
-        accessors = self.parse_expression(expr, instance_path, base_context)
-        state_ref: StateProxy = self.wf.user_state
-        leaf_state_ref: StateProxy = state_ref
-
-        for accessor in accessors[:-1]:
-            if isinstance(state_ref, StateProxy):
-                leaf_state_ref = state_ref
-
-            if isinstance(state_ref, list):
-                state_ref = state_ref[int(accessor)]
-            else:
-                state_ref = state_ref[accessor]
-
-        if not isinstance(state_ref, (StateProxy, dict)):
-            raise ValueError(
-                f"Incorrect state reference. Reference \"{expr}\" isn't part of a StateProxy or dict.")
-
-        state_ref[accessors[-1]] = value
-        leaf_state_ref.apply_mutation_marker(recursive=True)
-
-    def parse_expression(self, expr: str, instance_path: Optional[InstancePath] = None, base_context = {}) -> List[str]:
-
-        """ Returns a list of accessors from an expression. """
-
-        accessors: List[str] = []
-        s = ""
-        level = 0
-
-        i = 0
-        while i < len(expr):
-            character = expr[i]
-            if character == "\\":
-                if i + 1 < len(expr):
-                    s += expr[i + 1]
-                    i += 1
-            elif character == ".":
-                if level == 0:
-                    accessors.append(s)
-                    s = ""
-                else:
-                    s += character
-            elif character == "[":
-                if level == 0:
-                    accessors.append(s)
-                    s = ""
-                else:
-                    s += character
-                level += 1
-            elif character == "]":
-                level -= 1
-                if level == 0:
-                    s = str(self.evaluate_expression(s, instance_path, base_context))
-                else:
-                    s += character
-            else:
-                s += character
-
-            i += 1
-
-        if s:
-            accessors.append(s)
-
-        return accessors
-
-    def get_env_variable_value(self, expr: str):
-        return os.getenv(expr[1:])
-
-    def evaluate_expression(self, expr: str, instance_path: Optional[InstancePath] = None, base_context = {}) -> Any:
-        context_data = base_context
-        result = None
-        if instance_path:
-            context_data = self.get_context_data(instance_path, base_context)
-        context_ref: Any = context_data
-        state_ref: Any = self.wf.user_state.state
-        accessors: List[str] = self.parse_expression(expr, instance_path, base_context)
-
-        for accessor in accessors:
-            if isinstance(state_ref, (StateProxy, dict)) and accessor in state_ref:
-                state_ref = state_ref.get(accessor)
-                result = state_ref
-            elif isinstance(state_ref, (list)) and state_ref[int(accessor)] is not None:
-                state_ref = state_ref[int(accessor)]
-                result = state_ref
-            elif isinstance(context_ref, dict) and accessor in context_ref:
-                context_ref = context_ref.get(accessor)
-                result = context_ref
-
-        if isinstance(result, StateProxy):
-            return result.to_dict()
-
-        if result is None and expr.startswith("$"):
-            return self.get_env_variable_value(expr)
-
-        return result
-
-
-class WriterSession:
-
-    """
-    Represents a session.
-    """
-
-    def __init__(self, session_id: str, cookies: Optional[Dict[str, str]], headers: Optional[Dict[str, str]]) -> None:
-        self.session_id = session_id
-        self.cookies = cookies
-        self.headers = headers
-        self.last_active_timestamp: int = int(time.time())
-        new_state = WriterState.get_new()
-        new_state.user_state.mutated = set()
-        self.session_state = new_state
-        self.session_component_tree = core_ui.build_session_component_tree(base_component_tree)
-        self.event_handler = EventHandler(self)
-        self.userinfo: Optional[dict] = None
-
-    def update_last_active_timestamp(self) -> None:
-        self.last_active_timestamp = int(time.time())
-
-
 class SessionManager:
 
     """
@@ -1767,11 +1571,14 @@ class EventHandler:
     """
 
     def __init__(self, session: WriterSession) -> None:
+        import writer.workflows
+
         self.session = session
         self.session_state = session.session_state
         self.session_component_tree = session.session_component_tree
-        self.deser = EventDeserialiser(self.session_state, self.session_component_tree)
-        self.evaluator = Evaluator(self.session_state, self.session_component_tree)
+        self.deser = EventDeserialiser(session)
+        self.evaluator = writer.evaluator.Evaluator(session.session_state, session.session_component_tree)
+        self.workflow_runner = writer.workflows.WorkflowRunner(session)
 
 
     def _handle_binding(self, event_type, target_component, instance_path, payload) -> None:
@@ -1784,15 +1591,15 @@ def _handle_binding(self, event_type, target_component, instance_path, payload)
 
     def _get_workflow_callable(self, workflow_key: Optional[str], workflow_id: Optional[str]):
         def fn(payload, context, session):
-            execution_env = {
+            execution_environment = {
                 "payload": payload,
                 "context": context,
                 "session": session
             }
             if workflow_key:
-                writer.workflows.run_workflow_by_key(self.session, workflow_key, execution_env)
+                self.workflow_runner.run_workflow_by_key(workflow_key, execution_environment)
             elif workflow_id:
-                writer.workflows.run_workflow(self.session, workflow_id, execution_env)                
+                self.workflow_runner.run_workflow(workflow_id, execution_environment, "Workflow execution triggered on demand")
         return fn
 
     def _get_handler_callable(self, target_component: Component, event_type: str) -> Optional[Callable]:        
@@ -1819,7 +1626,7 @@ def _call_handler_callable(
         self,
         event_type: str,
         target_component: Component,
-        instance_path: List[InstancePathItem],
+        instance_path: InstancePath,
         payload: Any
     ) -> Any:
         
@@ -1845,7 +1652,7 @@ def _call_handler_callable(
         with core_ui.use_component_tree(self.session.session_component_tree), \
             contextlib.redirect_stdout(io.StringIO()) as f:
             middlewares_executors = current_app_process.middleware_registry.executors()
-            result = writer_event_handler_invoke_with_middlewares(middlewares_executors, handler_callable, writer_args)
+            result = EventHandlerExecutor.invoke_with_middlewares(middlewares_executors, handler_callable, writer_args)
             captured_stdout = f.getvalue()
 
         if captured_stdout:
@@ -1886,6 +1693,80 @@ def handle(self, ev: WriterEvent) -> WriterEventResult:
 
         return {"ok": ok, "result": result}
 
+class EventHandlerExecutor:
+
+    @staticmethod
+    def build_arguments(func: Callable, writer_args: dict) -> List[Any]:
+        """
+        Constructs the list of arguments based on the signature of the function
+        which can be a handler or middleware.
+
+        >>> def my_event_handler(state, context):
+        >>>     yield
+
+        >>> args = EventHandlerExecutor.build_arguments(my_event_handler, {'state': {}, 'payload': {}, 'context': {"target": '11'}, 'session': None, 'ui': None})
+        >>> [{}, {"target": '11'}]
+
+        :param func: the function that will be called
+        :param writer_args: the possible arguments in writer (state, payload, ...)
+        """
+        handler_args = inspect.getfullargspec(func).args
+        func_args = []
+        for arg in handler_args:
+            if arg in writer_args:
+                func_args.append(writer_args[arg])
+
+        return func_args
+
+    @staticmethod
+    def invoke(callable_handler: Callable, writer_args: dict) -> Any:
+        """
+        Runs a handler based on its signature.
+
+        If the handler is asynchronous, it is executed asynchronously.
+        If the handler only has certain parameters, only these are passed as arguments
+
+        >>> def my_handler(state):
+        >>>     state['a'] = 2
+        >>>
+        >>> EventHandlerExecutor.invoke(my_handler, {'state': {'a': 1}, 'payload': None, 'context': None, 'session': None, 'ui': None})
+        """
+        is_async_handler = inspect.iscoroutinefunction(callable_handler)
+        if (not callable(callable_handler) and not is_async_handler):
+            raise ValueError("Invalid handler. The handler isn't a callable object.")
+
+        handler_args = EventHandlerExecutor.build_arguments(callable_handler, writer_args)
+
+        if is_async_handler:
+            async_wrapper = _async_wrapper_internal(callable_handler, handler_args)
+            result = asyncio.run(async_wrapper)
+        else:
+            result = callable_handler(*handler_args)
+
+        return result
+
+    @staticmethod
+    def invoke_with_middlewares(middlewares_executors: List[MiddlewareExecutor], callable_handler: Callable, writer_args: dict) -> Any:
+        """
+        Runs the middlewares then the handler. This function allows you to manage exceptions that are triggered in middleware
+
+        :param middlewares_executors: The list of middleware to run
+        :param callable_handler: The target handler
+
+        >>> @wf.middleware()
+        >>> def my_middleware(state, payload, context, session, ui):
+        >>>     yield
+
+        >>> executor = MiddlewareExecutor(my_middleware, {'state': {}, 'payload': None, 'context': None, 'session': None, 'ui': None})
+        >>> EventHandlerExecutor.invoke_with_middlewares([executor], my_handler, {'state': {}, 'payload': None, 'context': None, 'session': None, 'ui': None}
+        """
+        if len(middlewares_executors) == 0:
+            return EventHandlerExecutor.invoke(callable_handler, writer_args)
+        else:
+            executor = middlewares_executors[0]
+            with executor.execute(writer_args):
+                return EventHandlerExecutor.invoke_with_middlewares(middlewares_executors[1:], callable_handler, writer_args)
+
 
 class DictPropertyProxy:
     """
@@ -1933,412 +1814,6 @@ def __set__(self, instance, value):
         proxy[self.key] = value
 
 
-class DataframeRecordRemove:
-    pass
-
-
-class DataframeRecordProcessor():
-    """
-    This interface defines the signature of the methods to process the events of a
-    dataframe compatible with EditableDataframe.
-
-    A Dataframe can be any structure composed of tabular data.
-
-    This class defines the signature of the methods to be implemented.
-    """
-    __metaclass__ = ABCMeta
-
-    @staticmethod
-    def match(df: Any) -> bool:
-        """
-        This method checks if the dataframe is compatible with the processor.
-        """
-        raise NotImplementedError
-
-    @staticmethod
-    def record(df: Any, record_index: int) -> dict:
-        """
-        This method read a record at the given line and get it back as dictionary
-
-        >>> edf = EditableDataframe(df)
-        >>> r = edf.record(1)
-        """
-        raise NotImplementedError
-
-    @staticmethod
-    def record_add(df: Any, payload: DataframeRecordAdded) -> Any:
-        """
-        signature of the methods to be implemented to process wf-dataframe-add event
-
-        >>> edf = EditableDataframe(df)
-        >>> edf.record_add({"record": {"a": 1, "b": 2}})
-        """
-        raise NotImplementedError
-
-    @staticmethod
-    def record_update(df: Any, payload: DataframeRecordUpdated) -> Any:
-        """
-        signature of the methods to be implemented to process wf-dataframe-update event
-
-        >>> edf = EditableDataframe(df)
-        >>> edf.record_update({"record_index": 12, "record": {"a": 1, "b": 2}})
-        """
-        raise NotImplementedError
-
-    @staticmethod
-    def record_remove(df: Any, payload: DataframeRecordRemoved) -> Any:
-        """
-        signature of the methods to be implemented to process wf-dataframe-action event
-
-        >>> edf = EditableDataframe(df)
-        >>> edf.record_remove({"record_index": 12})
-        """
-        raise NotImplementedError
-
-    @staticmethod
-    def pyarrow_table(df: Any) -> pyarrow.Table:
-        """
-        Serializes the dataframe into a pyarrow table
-        """
-        raise NotImplementedError
-
-
-class PandasRecordProcessor(DataframeRecordProcessor):
-    """
-    PandasRecordProcessor processes records from a pandas dataframe saved into an EditableDataframe
-
-    >>> df = pandas.DataFrame({"a": [1, 2], "b": [3, 4]})
-    >>> edf = EditableDataframe(df)
-    >>> edf.record_add({"a": 1, "b": 2})
-    """
-
-    @staticmethod
-    @import_failure(rvalue=False)
-    def match(df: Any) -> bool:
-        import pandas
-        return True if isinstance(df, pandas.DataFrame) else False
-
-    @staticmethod
-    def record(df: 'pandas.DataFrame', record_index: int) -> dict:
-        """
-
-        >>> edf = EditableDataframe(df)
-        >>> r = edf.record(1)
-        """
-        import pandas
-
-        record = df.iloc[record_index]
-        if not isinstance(df.index, pandas.RangeIndex):
-            index_list = df.index.tolist()
-            record_index_content = index_list[record_index]
-            if isinstance(record_index_content, tuple):
-                for i, n in enumerate(df.index.names):
-                    record[n] = record_index_content[i]
-            else:
-                record[df.index.names[0]] = record_index_content
-
-        return dict(record)
-
-    @staticmethod
-    def record_add(df: 'pandas.DataFrame', payload: DataframeRecordAdded) -> 'pandas.DataFrame':
-        """
-        >>> edf = EditableDataframe(df)
-        >>> edf.record_add({"record": {"a": 1, "b": 2}})
-        """
-        import pandas
-
-        _assert_record_match_pandas_df(df, payload['record'])
-
-        record, index = _split_record_as_pandas_record_and_index(payload['record'], df.index.names)
-
-        if isinstance(df.index, pandas.RangeIndex):
-            new_df = pandas.DataFrame([record])
-            return pandas.concat([df, new_df], ignore_index=True)
-        else:
-            new_df = pandas.DataFrame([record], index=[index])
-            return pandas.concat([df, new_df])
-
-    @staticmethod
-    def record_update(df: 'pandas.DataFrame', payload: DataframeRecordUpdated) -> 'pandas.DataFrame':
-        """
-        >>> edf = EditableDataframe(df)
-        >>> edf.record_update({"record_index": 12, "record": {"a": 1, "b": 2}})
-        """
-        import pandas
-
-        _assert_record_match_pandas_df(df, payload['record'])
-
-        record: dict
-        record, index = _split_record_as_pandas_record_and_index(payload['record'], df.index.names)
-
-        record_index = payload['record_index']
-
-        if isinstance(df.index, pandas.RangeIndex):
-            df.iloc[record_index] = record  # type: ignore
-        else:
-            df.iloc[record_index] = record  # type: ignore
-            index_list = df.index.tolist()
-            index_list[record_index] = index
-            df.index = index_list  # type: ignore
-
-        return df
-
-    @staticmethod
-    def record_remove(df: 'pandas.DataFrame', payload: DataframeRecordRemoved) -> 'pandas.DataFrame':
-        """
-        >>> edf = EditableDataframe(df)
-        >>> edf.record_remove({"record_index": 12})
-        """
-        record_index: int = payload['record_index']
-        idx = df.index[record_index]
-        df = df.drop(idx)
-
-        return df
-
-    @staticmethod
-    def pyarrow_table(df: 'pandas.DataFrame') -> pyarrow.Table:
-        """
-        Serializes the dataframe into a pyarrow table
-        """
-        table = pyarrow.Table.from_pandas(df=df)
-        return table
-
-
-class PolarRecordProcessor(DataframeRecordProcessor):
-    """
-    PolarRecordProcessor processes records from a polar dataframe saved into an EditableDataframe
-
-    >>> df = polars.DataFrame({"a": [1, 2], "b": [3, 4]})
-    >>> edf = EditableDataframe(df)
-    >>> edf.record_add({"record": {"a": 1, "b": 2}})
-    """
-
-    @staticmethod
-    @import_failure(rvalue=False)
-    def match(df: Any) -> bool:
-        import polars
-        return True if isinstance(df, polars.DataFrame) else False
-
-    @staticmethod
-    def record(df: 'polars.DataFrame', record_index: int) -> dict:
-        """
-
-        >>> edf = EditableDataframe(df)
-        >>> r = edf.record(1)
-        """
-        record = {}
-        r = df[record_index]
-        for c in r.columns:
-            record[c] = df[record_index, c]
-
-        return record
-
-
-    @staticmethod
-    def record_add(df: 'polars.DataFrame', payload: DataframeRecordAdded) -> 'polars.DataFrame':
-        _assert_record_match_polar_df(df, payload['record'])
-
-        import polars
-        new_df = polars.DataFrame([payload['record']])
-        return polars.concat([df, new_df])
-
-    @staticmethod
-    def record_update(df: 'polars.DataFrame', payload: DataframeRecordUpdated) -> 'polars.DataFrame':
-        # This implementation works but is not optimal.
-        # I didn't find a better way to update a record in polars
-        #
-        # https://github.com/pola-rs/polars/issues/5973
-        _assert_record_match_polar_df(df, payload['record'])
-
-        record = payload['record']
-        record_index = payload['record_index']
-        for r in record:
-            df[record_index, r] = record[r]
-
-        return df
-
-    @staticmethod
-    def record_remove(df: 'polars.DataFrame', payload: DataframeRecordRemoved) -> 'polars.DataFrame':
-        import polars
-
-        record_index: int = payload['record_index']
-        df_filtered = polars.concat([df[:record_index], df[record_index + 1:]])
-        return df_filtered
-
-    @staticmethod
-    def pyarrow_table(df: 'polars.DataFrame') -> pyarrow.Table:
-        """
-        Serializes the dataframe into a pyarrow table
-        """
-        import pyarrow.interchange
-        table: pyarrow.Table = pyarrow.interchange.from_dataframe(df)
-        return table
-
-class RecordListRecordProcessor(DataframeRecordProcessor):
-    """
-    RecordListRecordProcessor processes records from a list of record saved into an EditableDataframe
-
-    >>> df = [{"a": 1, "b": 2}, {"a": 3, "b": 4}]
-    >>> edf = EditableDataframe(df)
-    >>> edf.record_add({"record": {"a": 1, "b": 2}})
-    """
-
-    @staticmethod
-    def match(df: Any) -> bool:
-        return True if isinstance(df, list) else False
-
-
-    @staticmethod
-    def record(df: List[Dict[str, Any]], record_index: int) -> dict:
-        """
-
-        >>> edf = EditableDataframe(df)
-        >>> r = edf.record(1)
-        """
-        r = df[record_index]
-        return copy.copy(r)
-
-    @staticmethod
-    def record_add(df: List[Dict[str, Any]], payload: DataframeRecordAdded) -> List[Dict[str, Any]]:
-        _assert_record_match_list_of_records(df, payload['record'])
-        df.append(payload['record'])
-        return df
-
-    @staticmethod
-    def record_update(df: List[Dict[str, Any]], payload: DataframeRecordUpdated) -> List[Dict[str, Any]]:
-        _assert_record_match_list_of_records(df, payload['record'])
-
-        record_index = payload['record_index']
-        record = payload['record']
-
-        df[record_index] = record
-        return df
-
-    @staticmethod
-    def record_remove(df: List[Dict[str, Any]], payload: DataframeRecordRemoved) -> List[Dict[str, Any]]:
-        del(df[payload['record_index']])
-        return df
-
-    @staticmethod
-    def pyarrow_table(df: List[Dict[str, Any]]) -> pyarrow.Table:
-        """
-        Serializes the dataframe into a pyarrow table
-        """
-        column_names = list(df[0].keys())
-        columns = {key: [record[key] for record in df] for key in column_names}
-
-        pyarrow_columns = {key: pyarrow.array(values) for key, values in columns.items()}
-        schema = pyarrow.schema([(key, pyarrow_columns[key].type) for key in pyarrow_columns])
-        table = pyarrow.Table.from_arrays(
-            [pyarrow_columns[key] for key in column_names],
-            schema=schema
-        )
-
-        return table
-
-class EditableDataframe(MutableValue):
-    """
-    Editable Dataframe makes it easier to process events from components
-    that modify a dataframe like the dataframe editor.
-
-    >>> initial_state = wf.init_state({
-    >>>    "df": wf.EditableDataframe(df)
-    >>> })
-
-    Editable Dataframe is compatible with a pandas, thrillers or record list dataframe
-    """
-    processors = [PandasRecordProcessor, PolarRecordProcessor, RecordListRecordProcessor]
-
-    def __init__(self, df: Union['pandas.DataFrame', 'polars.DataFrame', List[dict]]):
-        super().__init__()
-        self._df = df
-        self.processor: Type[DataframeRecordProcessor]
-        for processor in self.processors:
-            if processor.match(self.df):
-                self.processor = processor
-                break
-
-        if self.processor is None:
-            raise ValueError("The dataframe must be a pandas, polar Dataframe or a list of record")
-
-    @property
-    def df(self) -> Union['pandas.DataFrame', 'polars.DataFrame', List[dict]]:
-        return self._df
-
-    @df.setter
-    def df(self, value: Union['pandas.DataFrame', 'polars.DataFrame', List[dict]]) -> None:
-        self._df = value
-        self.mutate()
-
-    def record_add(self, payload: DataframeRecordAdded) -> None:
-        """
-        Adds a record to the dataframe
-
-        >>> df = pandas.DataFrame({"a": [1, 2], "b": [3, 4]})
-        >>> edf = EditableDataframe(df)
-        >>> edf.record_add({"record": {"a": 1, "b": 2}})
-        """
-        assert self.processor is not None
-
-        self._df = self.processor.record_add(self.df, payload)
-        self.mutate()
-
-    def record_update(self, payload: DataframeRecordUpdated) -> None:
-        """
-        Updates a record in the dataframe
-
-        The record must be complete otherwise an error is raised (ValueError).
-        It must a value for each index / column.
-
-        >>> df = pandas.DataFrame({"a": [1, 2], "b": [3, 4]})
-        >>> edf = EditableDataframe(df)
-        >>> edf.record_update({"record_index": 0, "record": {"a": 2, "b": 2}})
-        """
-        assert self.processor is not None
-
-        self._df = self.processor.record_update(self.df, payload)
-        self.mutate()
-
-    def record_remove(self, payload: DataframeRecordRemoved) -> None:
-        """
-        Removes a record from the dataframe
-
-        >>> df = pandas.DataFrame({"a": [1, 2], "b": [3, 4]})
-        >>> edf = EditableDataframe(df)
-        >>> edf.record_remove({"record_index": 0})
-        """
-        assert self.processor is not None
-
-        self._df = self.processor.record_remove(self.df, payload)
-        self.mutate()
-
-    def pyarrow_table(self) -> pyarrow.Table:
-        """
-        Serializes the dataframe into a pyarrow table
-
-        This mechanism is used for serializing data for transmission to the frontend.
-
-        >>> df = pandas.DataFrame({"a": [1, 2], "b": [3, 4]})
-        >>> edf = EditableDataframe(df)
-        >>> pa_table = edf.pyarrow_table()
-        """
-        assert self.processor is not None
-
-        pa_table = self.processor.pyarrow_table(self.df)
-        return pa_table
-
-    def record(self, record_index: int):
-        """
-        Retrieves a specific record in dictionary form.
-
-        :param record_index:
-        :return:
-        """
-        assert self.processor is not None
-
-        record = self.processor.record(self.df, record_index)
-        return record
-
 S = TypeVar("S", bound=WriterState)
 
 def new_initial_state(klass: Type[S], raw_state: dict) -> S:
@@ -2523,119 +1998,10 @@ def parse_state_variable_expression(p: str):
     return parts
 
 
-def writer_event_handler_build_arguments(func: Callable, writer_args: dict) -> List[Any]:
-    """
-    Constructs the list of arguments based on the signature of the function
-    which can be a handler or middleware.
-
-    >>> def my_event_handler(state, context):
-    >>>     yield
-
-    >>> args = writer_event_handler_build_arguments(my_event_handler, {'state': {}, 'payload': {}, 'context': {"target": '11'}, 'session': None, 'ui': None})
-    >>> [{}, {"target": '11'}]
-
-    :param func: the function that will be called
-    :param writer_args: the possible arguments in writer (state, payload, ...)
-    """
-    handler_args = inspect.getfullargspec(func).args
-    func_args = []
-    for arg in handler_args:
-        if arg in writer_args:
-            func_args.append(writer_args[arg])
-
-    return func_args
-
-
-def writer_event_handler_invoke(callable_handler: Callable, writer_args: dict) -> Any:
-    """
-    Runs a handler based on its signature.
-
-    If the handler is asynchronous, it is executed asynchronously.
-    If the handler only has certain parameters, only these are passed as arguments
-
-    >>> def my_handler(state):
-    >>>     state['a'] = 2
-    >>>
-    >>> writer_event_handler_invoke(my_handler, {'state': {'a': 1}, 'payload': None, 'context': None, 'session': None, 'ui': None})
-    """
-    is_async_handler = inspect.iscoroutinefunction(callable_handler)
-    if (not callable(callable_handler) and not is_async_handler):
-        raise ValueError("Invalid handler. The handler isn't a callable object.")
-
-    handler_args = writer_event_handler_build_arguments(callable_handler, writer_args)
-
-    if is_async_handler:
-        async_wrapper = _async_wrapper_internal(callable_handler, handler_args)
-        result = asyncio.run(async_wrapper)
-    else:
-        result = callable_handler(*handler_args)
-
-    return result
-
-def writer_event_handler_invoke_with_middlewares(middlewares_executors: List[MiddlewareExecutor], callable_handler: Callable, writer_args: dict) -> Any:
-    """
-    Runs the middlewares then the handler. This function allows you to manage exceptions that are triggered in middleware
-
-    :param middlewares_executors: The list of middleware to run
-    :param callable_handler: The target handler
-
-    >>> @wf.middleware()
-    >>> def my_middleware(state, payload, context, session, ui):
-    >>>     yield
-
-    >>> executor = MiddlewareExecutor(my_middleware, {'state': {}, 'payload': None, 'context': None, 'session': None, 'ui': None})
-    >>> writer_event_handler_invoke_with_middlewares([executor], my_handler, {'state': {}, 'payload': None, 'context': None, 'session': None, 'ui': None}
-    """
-    if len(middlewares_executors) == 0:
-        return writer_event_handler_invoke(callable_handler, writer_args)
-    else:
-        executor = middlewares_executors[0]
-        with executor.execute(writer_args):
-            return writer_event_handler_invoke_with_middlewares(middlewares_executors[1:], callable_handler, writer_args)
-
-
 async def _async_wrapper_internal(callable_handler: Callable, arg_values: List[Any]) -> Any:
     result = await callable_handler(*arg_values)
     return result
 
-def _assert_record_match_pandas_df(df: 'pandas.DataFrame', record: Dict[str, Any]) -> None:
-    """
-    Asserts that the record matches the dataframe columns & index
-
-    >>> _assert_record_match_pandas_df(pandas.DataFrame({"a": [1, 2], "b": [3, 4]}), {"a": 1, "b": 2})
-    """
-    import pandas
-
-    columns = set(list(df.columns.values) + df.index.names) if isinstance(df.index, pandas.RangeIndex) is False else set(df.columns.values)
-    columns_record = set(record.keys())
-    if columns != columns_record:
-        raise ValueError(f"Columns mismatch. Expected {columns}, got {columns_record}")
-
-def _assert_record_match_polar_df(df: 'polars.DataFrame', record: Dict[str, Any]) -> None:
-    """
-    Asserts that the record matches the columns of polar dataframe
-
-    >>> _assert_record_match_pandas_df(polars.DataFrame({"a": [1, 2], "b": [3, 4]}), {"a": 1, "b": 2})
-    """
-    columns = set(df.columns)
-    columns_record = set(record.keys())
-    if columns != columns_record:
-        raise ValueError(f"Columns mismatch. Expected {columns}, got {columns_record}")
-
-def _assert_record_match_list_of_records(df: List[Dict[str, Any]], record: Dict[str, Any]) -> None:
-    """
-    Asserts that the record matches the key in the record list (it use the first record to check)
-
-    >>> _assert_record_match_list_of_records([{"a": 1, "b": 2}, {"a": 3, "b": 4}], {"a": 1, "b": 2})
-    """
-    if len(df) == 0:
-        return
-
-    columns = set(df[0].keys())
-    columns_record = set(record.keys())
-    if columns != columns_record:
-        raise ValueError(f"Columns mismatch. Expected {columns}, got {columns_record}")
-
 def _event_handler_session_info() -> Dict[str, Any]:
     """
     Returns the session information for the current event handler.
@@ -2661,26 +2027,6 @@ def _event_handler_ui_manager():
     else:
         raise RuntimeError(_get_ui_runtime_error_message())
 
-
-def _split_record_as_pandas_record_and_index(param: dict, index_columns: list) -> Tuple[dict, tuple]:
-    """
-    Separates a record into the record part and the index part to be able to
-    create or update a row in a dataframe.
-
-    >>> record, index = _split_record_as_pandas_record_and_index({"a": 1, "b": 2}, ["a"])
-    >>> print(record) # {"b": 2}
-    >>> print(index) # (1,)
-    """
-    final_record = {}
-    final_index = []
-    for key, value in param.items():
-        if key in index_columns:
-            final_index.append(value)
-        else:
-            final_record[key] = value
-
-    return final_record, tuple(final_index)
-
 def _deserialize_bigint_format(payload: Optional[Union[dict, list]]):
     """
     Decodes the payload of a big int serialization
diff --git a/src/writer/core_df.py b/src/writer/core_df.py
new file mode 100644
index 000000000..f5e694798
--- /dev/null
+++ b/src/writer/core_df.py
@@ -0,0 +1,479 @@
+"""
+`core_df` contains classes and functions that allow you to manipulate editable dataframes.
+"""
+import copy
+from abc import ABCMeta
+from typing import TYPE_CHECKING, Any, Dict, List, Tuple, Type, Union
+
+import pyarrow  # type: ignore
+
+from .core import MutableValue, import_failure
+from .ss_types import DataframeRecordAdded, DataframeRecordRemoved, DataframeRecordUpdated
+
+if TYPE_CHECKING:
+    import pandas
+    import polars
+
+
+class DataframeRecordProcessor():
+    """
+    This interface defines the signature of the methods to process the events of a
+    dataframe compatible with EditableDataframe.
+
+    A Dataframe can be any structure composed of tabular data.
+
+    This class defines the signature of the methods to be implemented.
+    """
+    __metaclass__ = ABCMeta
+
+    @staticmethod
+    def match(df: Any) -> bool:
+        """
+        This method checks if the dataframe is compatible with the processor.
+        """
+        raise NotImplementedError
+
+    @staticmethod
+    def record(df: Any, record_index: int) -> dict:
+        """
+        This method read a record at the given line and get it back as dictionary
+
+        >>> edf = EditableDataframe(df)
+        >>> r = edf.record(1)
+        """
+        raise NotImplementedError
+
+    @staticmethod
+    def record_add(df: Any, payload: DataframeRecordAdded) -> Any:
+        """
+        signature of the methods to be implemented to process wf-dataframe-add event
+
+        >>> edf = EditableDataframe(df)
+        >>> edf.record_add({"record": {"a": 1, "b": 2}})
+        """
+        raise NotImplementedError
+
+    @staticmethod
+    def record_update(df: Any, payload: DataframeRecordUpdated) -> Any:
+        """
+        signature of the methods to be implemented to process wf-dataframe-update event
+
+        >>> edf = EditableDataframe(df)
+        >>> edf.record_update({"record_index": 12, "record": {"a": 1, "b": 2}})
+        """
+        raise NotImplementedError
+
+    @staticmethod
+    def record_remove(df: Any, payload: DataframeRecordRemoved) -> Any:
+        """
+        signature of the methods to be implemented to process wf-dataframe-action event
+
+        >>> edf = EditableDataframe(df)
+        >>> edf.record_remove({"record_index": 12})
+        """
+        raise NotImplementedError
+
+    @staticmethod
+    def pyarrow_table(df: Any) -> pyarrow.Table:
+        """
+        Serializes the dataframe into a pyarrow table
+        """
+        raise NotImplementedError
+
+
+class PandasRecordProcessor(DataframeRecordProcessor):
+    """
+    PandasRecordProcessor processes records from a pandas dataframe saved into an EditableDataframe
+
+    >>> df = pandas.DataFrame({"a": [1, 2], "b": [3, 4]})
+    >>> edf = EditableDataframe(df)
+    >>> edf.record_add({"a": 1, "b": 2})
+    """
+
+    @staticmethod
+    @import_failure(rvalue=False)
+    def match(df: Any) -> bool:
+        import pandas
+        return True if isinstance(df, pandas.DataFrame) else False
+
+    @staticmethod
+    def record(df: 'pandas.DataFrame', record_index: int) -> dict:
+        """
+
+        >>> edf = EditableDataframe(df)
+        >>> r = edf.record(1)
+        """
+        import pandas
+
+        record = df.iloc[record_index]
+        if not isinstance(df.index, pandas.RangeIndex):
+            index_list = df.index.tolist()
+            record_index_content = index_list[record_index]
+            if isinstance(record_index_content, tuple):
+                for i, n in enumerate(df.index.names):
+                    record[n] = record_index_content[i]
+            else:
+                record[df.index.names[0]] = record_index_content
+
+        return dict(record)
+
+    @staticmethod
+    def record_add(df: 'pandas.DataFrame', payload: DataframeRecordAdded) -> 'pandas.DataFrame':
+        """
+        >>> edf = EditableDataframe(df)
+        >>> edf.record_add({"record": {"a": 1, "b": 2}})
+        """
+        import pandas
+
+        _assert_record_match_pandas_df(df, payload['record'])
+
+        record, index = _split_record_as_pandas_record_and_index(payload['record'], df.index.names)
+
+        if isinstance(df.index, pandas.RangeIndex):
+            new_df = pandas.DataFrame([record])
+            return pandas.concat([df, new_df], ignore_index=True)
+        else:
+            new_df = pandas.DataFrame([record], index=[index])
+            return pandas.concat([df, new_df])
+
+    @staticmethod
+    def record_update(df: 'pandas.DataFrame', payload: DataframeRecordUpdated) -> 'pandas.DataFrame':
+        """
+        >>> edf = EditableDataframe(df)
+        >>> edf.record_update({"record_index": 12, "record": {"a": 1, "b": 2}})
+        """
+        import pandas
+
+        _assert_record_match_pandas_df(df, payload['record'])
+
+        record: dict
+        record, index = _split_record_as_pandas_record_and_index(payload['record'], df.index.names)
+
+        record_index = payload['record_index']
+
+        if isinstance(df.index, pandas.RangeIndex):
+            df.iloc[record_index] = record  # type: ignore
+        else:
+            df.iloc[record_index] = record  # type: ignore
+            index_list = df.index.tolist()
+            index_list[record_index] = index
+            df.index = index_list  # type: ignore
+
+        return df
+
+    @staticmethod
+    def record_remove(df: 'pandas.DataFrame', payload: DataframeRecordRemoved) -> 'pandas.DataFrame':
+        """
+        >>> edf = EditableDataframe(df)
+        >>> edf.record_remove({"record_index": 12})
+        """
+        record_index: int = payload['record_index']
+        idx = df.index[record_index]
+        df = df.drop(idx)
+
+        return df
+
+    @staticmethod
+    def pyarrow_table(df: 'pandas.DataFrame') -> pyarrow.Table:
+        """
+        Serializes the dataframe into a pyarrow table
+        """
+        table = pyarrow.Table.from_pandas(df=df)
+        return table
+
+
+class PolarRecordProcessor(DataframeRecordProcessor):
+    """
+    PolarRecordProcessor processes records from a polar dataframe saved into an EditableDataframe
+
+    >>> df = polars.DataFrame({"a": [1, 2], "b": [3, 4]})
+    >>> edf = EditableDataframe(df)
+    >>> edf.record_add({"record": {"a": 1, "b": 2}})
+    """
+
+    @staticmethod
+    @import_failure(rvalue=False)
+    def match(df: Any) -> bool:
+        import polars
+        return True if isinstance(df, polars.DataFrame) else False
+
+    @staticmethod
+    def record(df: 'polars.DataFrame', record_index: int) -> dict:
+        """
+
+        >>> edf = EditableDataframe(df)
+        >>> r = edf.record(1)
+        """
+        record = {}
+        r = df[record_index]
+        for c in r.columns:
+            record[c] = df[record_index, c]
+
+        return record
+
+
+    @staticmethod
+    def record_add(df: 'polars.DataFrame', payload: DataframeRecordAdded) -> 'polars.DataFrame':
+        _assert_record_match_polar_df(df, payload['record'])
+
+        import polars
+        new_df = polars.DataFrame([payload['record']])
+        return polars.concat([df, new_df])
+
+    @staticmethod
+    def record_update(df: 'polars.DataFrame', payload: DataframeRecordUpdated) -> 'polars.DataFrame':
+        # This implementation works but is not optimal.
+        # I didn't find a better way to update a record in polars
+        #
+        # https://github.com/pola-rs/polars/issues/5973
+        _assert_record_match_polar_df(df, payload['record'])
+
+        record = payload['record']
+        record_index = payload['record_index']
+        for r in record:
+            df[record_index, r] = record[r]
+
+        return df
+
+    @staticmethod
+    def record_remove(df: 'polars.DataFrame', payload: DataframeRecordRemoved) -> 'polars.DataFrame':
+        import polars
+
+        record_index: int = payload['record_index']
+        df_filtered = polars.concat([df[:record_index], df[record_index + 1:]])
+        return df_filtered
+
+    @staticmethod
+    def pyarrow_table(df: 'polars.DataFrame') -> pyarrow.Table:
+        """
+        Serializes the dataframe into a pyarrow table
+        """
+        import pyarrow.interchange  # type: ignore
+        table: pyarrow.Table = pyarrow.interchange.from_dataframe(df)
+        return table
+
+class RecordListRecordProcessor(DataframeRecordProcessor):
+    """
+    RecordListRecordProcessor processes records from a list of record saved into an EditableDataframe
+
+    >>> df = [{"a": 1, "b": 2}, {"a": 3, "b": 4}]
+    >>> edf = EditableDataframe(df)
+    >>> edf.record_add({"record": {"a": 1, "b": 2}})
+    """
+
+    @staticmethod
+    def match(df: Any) -> bool:
+        return True if isinstance(df, list) else False
+
+
+    @staticmethod
+    def record(df: List[Dict[str, Any]], record_index: int) -> dict:
+        """
+
+        >>> edf = EditableDataframe(df)
+        >>> r = edf.record(1)
+        """
+        r = df[record_index]
+        return copy.copy(r)
+
+    @staticmethod
+    def record_add(df: List[Dict[str, Any]], payload: DataframeRecordAdded) -> List[Dict[str, Any]]:
+        _assert_record_match_list_of_records(df, payload['record'])
+        df.append(payload['record'])
+        return df
+
+    @staticmethod
+    def record_update(df: List[Dict[str, Any]], payload: DataframeRecordUpdated) -> List[Dict[str, Any]]:
+        _assert_record_match_list_of_records(df, payload['record'])
+
+        record_index = payload['record_index']
+        record = payload['record']
+
+        df[record_index] = record
+        return df
+
+    @staticmethod
+    def record_remove(df: List[Dict[str, Any]], payload: DataframeRecordRemoved) -> List[Dict[str, Any]]:
+        del(df[payload['record_index']])
+        return df
+
+    @staticmethod
+    def pyarrow_table(df: List[Dict[str, Any]]) -> pyarrow.Table:
+        """
+        Serializes the dataframe into a pyarrow table
+        """
+        column_names = list(df[0].keys())
+        columns = {key: [record[key] for record in df] for key in column_names}
+
+        pyarrow_columns = {key: pyarrow.array(values) for key, values in columns.items()}
+        schema = pyarrow.schema([(key, pyarrow_columns[key].type) for key in pyarrow_columns])
+        table = pyarrow.Table.from_arrays(
+            [pyarrow_columns[key] for key in column_names],
+            schema=schema
+        )
+
+        return table
+
+class EditableDataframe(MutableValue):
+    """
+    Editable Dataframe makes it easier to process events from components
+    that modify a dataframe like the dataframe editor.
+
+    >>> initial_state = wf.init_state({
+    >>>    "df": wf.EditableDataframe(df)
+    >>> })
+
+    Editable Dataframe is compatible with a pandas, thrillers or record list dataframe
+    """
+    processors = [PandasRecordProcessor, PolarRecordProcessor, RecordListRecordProcessor]
+
+    def __init__(self, df: Union['pandas.DataFrame', 'polars.DataFrame', List[dict]]):
+        super().__init__()
+        self._df = df
+        self.processor: Type[DataframeRecordProcessor]
+        for processor in self.processors:
+            if processor.match(self.df):
+                self.processor = processor
+                break
+
+        if self.processor is None:
+            raise ValueError("The dataframe must be a pandas, polar Dataframe or a list of record")
+
+    @property
+    def df(self) -> Union['pandas.DataFrame', 'polars.DataFrame', List[dict]]:
+        return self._df
+
+    @df.setter
+    def df(self, value: Union['pandas.DataFrame', 'polars.DataFrame', List[dict]]) -> None:
+        self._df = value
+        self.mutate()
+
+    def record_add(self, payload: DataframeRecordAdded) -> None:
+        """
+        Adds a record to the dataframe
+
+        >>> df = pandas.DataFrame({"a": [1, 2], "b": [3, 4]})
+        >>> edf = EditableDataframe(df)
+        >>> edf.record_add({"record": {"a": 1, "b": 2}})
+        """
+        assert self.processor is not None
+
+        self._df = self.processor.record_add(self.df, payload)
+        self.mutate()
+
+    def record_update(self, payload: DataframeRecordUpdated) -> None:
+        """
+        Updates a record in the dataframe
+
+        The record must be complete otherwise an error is raised (ValueError).
+        It must a value for each index / column.
+
+        >>> df = pandas.DataFrame({"a": [1, 2], "b": [3, 4]})
+        >>> edf = EditableDataframe(df)
+        >>> edf.record_update({"record_index": 0, "record": {"a": 2, "b": 2}})
+        """
+        assert self.processor is not None
+
+        self._df = self.processor.record_update(self.df, payload)
+        self.mutate()
+
+    def record_remove(self, payload: DataframeRecordRemoved) -> None:
+        """
+        Removes a record from the dataframe
+
+        >>> df = pandas.DataFrame({"a": [1, 2], "b": [3, 4]})
+        >>> edf = EditableDataframe(df)
+        >>> edf.record_remove({"record_index": 0})
+        """
+        assert self.processor is not None
+
+        self._df = self.processor.record_remove(self.df, payload)
+        self.mutate()
+
+    def pyarrow_table(self) -> pyarrow.Table:
+        """
+        Serializes the dataframe into a pyarrow table
+
+        This mechanism is used for serializing data for transmission to the frontend.
+
+        >>> df = pandas.DataFrame({"a": [1, 2], "b": [3, 4]})
+        >>> edf = EditableDataframe(df)
+        >>> pa_table = edf.pyarrow_table()
+        """
+        assert self.processor is not None
+
+        pa_table = self.processor.pyarrow_table(self.df)
+        return pa_table
+
+    def record(self, record_index: int):
+        """
+        Retrieves a specific record in dictionary form.
+
+        :param record_index:
+        :return:
+        """
+        assert self.processor is not None
+
+        record = self.processor.record(self.df, record_index)
+        return record
+
+
+
+def _assert_record_match_pandas_df(df: 'pandas.DataFrame', record: Dict[str, Any]) -> None:
+    """
+    Asserts that the record matches the dataframe columns & index
+
+    >>> _assert_record_match_pandas_df(pandas.DataFrame({"a": [1, 2], "b": [3, 4]}), {"a": 1, "b": 2})
+    """
+    import pandas
+
+    columns = set(list(df.columns.values) + df.index.names) if isinstance(df.index, pandas.RangeIndex) is False else set(df.columns.values)
+    columns_record = set(record.keys())
+    if columns != columns_record:
+        raise ValueError(f"Columns mismatch. Expected {columns}, got {columns_record}")
+
+def _assert_record_match_polar_df(df: 'polars.DataFrame', record: Dict[str, Any]) -> None:
+    """
+    Asserts that the record matches the columns of polar dataframe
+
+    >>> _assert_record_match_pandas_df(polars.DataFrame({"a": [1, 2], "b": [3, 4]}), {"a": 1, "b": 2})
+    """
+    columns = set(df.columns)
+    columns_record = set(record.keys())
+    if columns != columns_record:
+        raise ValueError(f"Columns mismatch. Expected {columns}, got {columns_record}")
+
+def _assert_record_match_list_of_records(df: List[Dict[str, Any]], record: Dict[str, Any]) -> None:
+    """
+    Asserts that the record matches the key in the record list (it use the first record to check)
+
+    >>> _assert_record_match_list_of_records([{"a": 1, "b": 2}, {"a": 3, "b": 4}], {"a": 1, "b": 2})
+    """
+    if len(df) == 0:
+        return
+
+    columns = set(df[0].keys())
+    columns_record = set(record.keys())
+    if columns != columns_record:
+        raise ValueError(f"Columns mismatch. Expected {columns}, got {columns_record}")
+
+
+
+def _split_record_as_pandas_record_and_index(param: dict, index_columns: list) -> Tuple[dict, tuple]:
+    """
+    Separates a record into the record part and the index part to be able to
+    create or update a row in a dataframe.
+
+    >>> record, index = _split_record_as_pandas_record_and_index({"a": 1, "b": 2}, ["a"])
+    >>> print(record) # {"b": 2}
+    >>> print(index) # (1,)
+    """
+    final_record = {}
+    final_index = []
+    for key, value in param.items():
+        if key in index_columns:
+            final_index.append(value)
+        else:
+            final_record[key] = value
+
+    return final_record, tuple(final_index)
diff --git a/src/writer/evaluator.py b/src/writer/evaluator.py
new file mode 100644
index 000000000..1d8ccf685
--- /dev/null
+++ b/src/writer/evaluator.py
@@ -0,0 +1,199 @@
+import json
+import os
+import re
+from typing import TYPE_CHECKING, Any, Dict, List, Optional, Tuple
+
+import writer.core
+import writer.core_ui
+from writer.ss_types import (
+    InstancePath,
+    WriterConfigurationError,
+)
+
+if TYPE_CHECKING:
+    from writer.core import WriterState
+    from writer.core_ui import ComponentTree
+
+
+class Evaluator:
+
+    """
+    Evaluates templates and expressions in the backend.
+    It allows for the sanitisation of frontend inputs.
+    """
+
+    TEMPLATE_REGEX = re.compile(r"[\\]?@{([^{]*?)}")
+
+    def __init__(self, state: "WriterState", component_tree: "ComponentTree"):
+        self.state = state
+        self.component_tree = component_tree
+        self.serializer = writer.core.StateSerialiser()
+
+    def evaluate_field(self, instance_path: InstancePath, field_key: str, as_json=False, default_field_value="", base_context={}) -> Any:
+        def decode_json(text):
+            try:
+                return json.loads(text)
+            except json.JSONDecodeError as exception:
+                raise WriterConfigurationError("Error decoding JSON. " + str(exception)) from exception
+
+        def replacer(matched):
+            if matched.string[0] == "\\":  # Escaped @, don't evaluate
+                return matched.string
+            expr = matched.group(1).strip()
+            expr_value = self.evaluate_expression(expr, instance_path, base_context)
+
+            return expr_value
+
+        component_id = instance_path[-1]["componentId"]
+        component = self.component_tree.get_component(component_id)
+        if not component:
+            raise ValueError(f'Component with id "{component_id}" not found.')
+
+        field_value = component.content.get(field_key) or default_field_value
+        replaced = None
+        full_match = self.TEMPLATE_REGEX.fullmatch(field_value)
+
+        if full_match is None:
+            replaced = self.TEMPLATE_REGEX.sub(lambda m: str(replacer(m)), field_value)
+            if as_json:
+                replaced = decode_json(replaced)
+        else:
+            replaced = replacer(full_match)
+            if as_json and isinstance(replaced, str):
+                replaced = decode_json(replaced)
+
+        return replaced
+
+
+    def get_context_data(self, instance_path: InstancePath, base_context={}) -> Dict[str, Any]:
+        context: Dict[str, Any] = base_context
+        for i in range(len(instance_path)):
+            path_item = instance_path[i]
+            component_id = path_item["componentId"]
+            component = self.component_tree.get_component(component_id)
+            if not component:
+                continue
+            if component.type != "repeater":
+                continue
+            if i + 1 >= len(instance_path):
+                continue
+            repeater_instance_path = instance_path[0:i+1]
+            next_instance_path = instance_path[0:i+2]
+            instance_number = next_instance_path[-1]["instanceNumber"]
+            repeater_object = self.evaluate_field(
+                repeater_instance_path, "repeaterObject", True, """{ "a": { "desc": "Option A" }, "b": { "desc": "Option B" } }""")
+            key_variable = self.evaluate_field(
+                repeater_instance_path, "keyVariable", False, "itemId")
+            value_variable = self.evaluate_field(
+                repeater_instance_path, "valueVariable", False, "item")
+
+            repeater_items: List[Tuple[Any, Any]] = []
+            if isinstance(repeater_object, dict):
+                repeater_items = list(repeater_object.items())
+            elif isinstance(repeater_object, list):
+                repeater_items = list(enumerate(repeater_object))
+            else:
+                raise ValueError(
+                    "Cannot produce context. Repeater object must evaluate to a dictionary.")
+
+            context[key_variable] = repeater_items[instance_number][0]
+            context[value_variable] = repeater_items[instance_number][1]
+
+        if len(instance_path) > 0:
+            context['target'] = instance_path[-1]['componentId']
+
+        return context
+
+    def set_state(self, expr: str, instance_path: InstancePath, value: Any, base_context = {}) -> None:
+        accessors = self.parse_expression(expr, instance_path, base_context)
+        state_ref = self.state
+
+        for accessor in accessors[:-1]:
+            if isinstance(state_ref, list):
+                state_ref = state_ref[int(accessor)]
+            else:
+                state_ref = state_ref[accessor]
+
+        if not isinstance(state_ref, (writer.core.State, writer.core.WriterState, writer.core.StateProxy, dict)):
+            raise ValueError(
+                f'Reference "{expr}" cannot be translated to state. Found value of type "{type(state_ref)}".')
+
+        state_ref[accessors[-1]] = value        
+
+    def parse_expression(self, expr: str, instance_path: Optional[InstancePath] = None, base_context = {}) -> List[str]:
+
+        """ Returns a list of accessors from an expression. """
+
+        if not isinstance(expr, str):
+            raise ValueError(f'Expression must be of type string. Value of type "{ type(expr) }" found.')
+
+        accessors: List[str] = []
+        s = ""
+        level = 0
+
+        i = 0
+        while i < len(expr):
+            character = expr[i]
+            if character == "\\":
+                if i + 1 < len(expr):
+                    s += expr[i + 1]
+                    i += 1
+            elif character == ".":
+                if level == 0:
+                    accessors.append(s)
+                    s = ""
+                else:
+                    s += character
+            elif character == "[":
+                if level == 0:
+                    accessors.append(s)
+                    s = ""
+                else:
+                    s += character
+                level += 1
+            elif character == "]":
+                level -= 1
+                if level == 0:
+                    s = str(self.evaluate_expression(s, instance_path, base_context))
+                else:
+                    s += character
+            else:
+                s += character
+
+            i += 1
+
+        if s:
+            accessors.append(s)
+
+        return accessors
+
+    def get_env_variable_value(self, expr: str):
+        return os.getenv(expr[1:])
+
+    def evaluate_expression(self, expr: str, instance_path: Optional[InstancePath] = None, base_context = {}) -> Any:
+        context_data = base_context
+        result = None
+        if instance_path:
+            context_data = self.get_context_data(instance_path, base_context)
+        context_ref: Any = context_data
+        state_ref: Any = self.state.user_state
+        accessors: List[str] = self.parse_expression(expr, instance_path, base_context)
+
+        for accessor in accessors:
+            if isinstance(state_ref, (writer.core.StateProxy, dict)) and accessor in state_ref:
+                state_ref = state_ref.get(accessor)
+                result = state_ref
+            elif isinstance(state_ref, (list)) and state_ref[int(accessor)] is not None:
+                state_ref = state_ref[int(accessor)]
+                result = state_ref
+            elif isinstance(context_ref, dict) and accessor in context_ref:
+                context_ref = context_ref.get(accessor)
+                result = context_ref
+
+        if isinstance(result, writer.core.StateProxy):
+            return result.to_dict()
+
+        if result is None and expr.startswith("$"):
+            return self.get_env_variable_value(expr)
+
+        return result
\ No newline at end of file
diff --git a/src/writer/ss_types.py b/src/writer/ss_types.py
index 397fe52d9..0cad40f6b 100644
--- a/src/writer/ss_types.py
+++ b/src/writer/ss_types.py
@@ -210,4 +210,8 @@ class ComponentDefinition(TypedDict):
     y: Optional[int]
 
 class WorkflowExecutionLog(BaseModel):
-    summary: List[Dict]
\ No newline at end of file
+    summary: List[Dict]
+
+
+class WriterConfigurationError(ValueError):
+    pass
\ No newline at end of file
diff --git a/src/writer/wf_project.py b/src/writer/wf_project.py
index 5987c5d83..61530b741 100644
--- a/src/writer/wf_project.py
+++ b/src/writer/wf_project.py
@@ -1,16 +1,21 @@
 """
 This module manipulates the folder of a wf project stored into `wf`.
 
->>> wf_project.write_files('app/hello', metadata={"writer_version": "0.1" }, components=...)
+>>> wf_project.write_files_async('app/hello', metadata={"writer_version": "0.1" }, components=...)
 
 >>> metadata, components = wf_project.read_files('app/hello')
 """
+import dataclasses
 import io
 import json
 import logging
+import multiprocessing
 import os
+import queue
+import time
 import typing
 from collections import OrderedDict
+from multiprocessing import Queue
 from typing import Any, Dict, List, Tuple
 
 from writer import core_ui
@@ -19,6 +24,26 @@
 ROOTS = ['root', 'workflows_root']
 COMPONENT_ROOTS = ['page', 'workflows_workflow']
 
+shared_queue_write_files: typing.Optional[Queue] = None
+
+@dataclasses.dataclass
+class WfProjectContext:
+    app_path: str
+    write_files_async_queue: Queue = Queue()
+    write_files_async_process: typing.Optional[multiprocessing.Process] = None
+    write_files_async_stop: Any = multiprocessing.Event() # Note: Event is a function, not a class in python, it can't be typed
+
+
+def write_files_async(context: WfProjectContext, metadata: MetadataDefinition, components: Dict[str, ComponentDefinition]) -> None:
+    """
+    This operation is asynchrone. It's managed in wf_project.process_write_files_async.
+
+    see wf_project.write_files for description
+
+    >>> wf_project.write_files_async('app/hello', metadata={"writer_version": "0.1" }, components=...)
+    """
+    context.write_files_async_queue.put((context.app_path, metadata, components))
+
 def write_files(app_path: str, metadata: MetadataDefinition, components: Dict[str, ComponentDefinition]) -> None:
     """
     Writes the meta data of the WF project to the `.wf` directory (metadata, components, ...).
@@ -31,6 +56,7 @@ def write_files(app_path: str, metadata: MetadataDefinition, components: Dict[st
 
     >>> wf_project.write_files('app/hello', metadata={"writer_version": "0.1" }, components=...)
     """
+
     wf_directory = os.path.join(app_path, ".wf")
     if not os.path.exists(wf_directory):
         os.makedirs(wf_directory)
@@ -43,6 +69,35 @@ def write_files(app_path: str, metadata: MetadataDefinition, components: Dict[st
     _remove_obsolete_component_files(wf_directory, components)
 
 
+def start_process_write_files_async(context: WfProjectContext, save_interval: float) -> None:
+    """
+    Creates a process that writes the .wf/ files
+
+    This agent allows you to process the backup of .wf files in the background
+    without blocking application requests.
+
+    :param wf_project_save_interval: the interval in seconds to save the project files
+    :return:
+    """
+    p = multiprocessing.Process(
+        target=_start_process_write_files_async_process,
+        args=(context, save_interval, context.write_files_async_stop)
+    )
+    context.write_files_async_process = p
+    p.start()
+
+
+def shutdown_process_write_files_async(context: WfProjectContext) -> None:
+    """
+    Shutdown the process that writes the .wf/ files
+    """
+    if context.write_files_async_process is not None and \
+        context.write_files_async_process.is_alive():
+        context.write_files_async_stop.set()
+        context.write_files_async_process.join()
+        context.write_files_async_process = None
+        context.write_files_async_stop.clear()
+
 def read_files(app_path: str) -> Tuple[MetadataDefinition, dict[str, ComponentDefinition]]:
     """
     Reads project files in the `.wf` folder.
@@ -221,3 +276,19 @@ def _hierarchical_position(components, c):
 
     return sorted(components.values(), key=lambda c: _hierarchical_position(components, c))
 
+
+def _start_process_write_files_async_process(context: WfProjectContext, save_interval, stop_event):
+    while True:
+        if stop_event.is_set():
+            break
+
+        try:
+            obj = context.write_files_async_queue.get(block=False)
+        except queue.Empty:
+            obj = None
+
+        if obj is not None:
+            app_path, metadata, components = obj
+            write_files(app_path, metadata, components)
+
+        time.sleep(save_interval)
diff --git a/src/writer/workflows.py b/src/writer/workflows.py
index e3266edc4..6e8275859 100644
--- a/src/writer/workflows.py
+++ b/src/writer/workflows.py
@@ -1,142 +1,183 @@
+import json
 import time
-from typing import Any, Dict, List, Literal, Optional, Tuple
+from typing import TYPE_CHECKING, Any, Dict, List, Literal, Optional, Tuple, Type
 
+import writer.blocks
+import writer.blocks.base_block
 import writer.core
-import writer.workflows_blocks
-from writer.core_ui import Component
-from writer.ss_types import WorkflowExecutionLog
-from writer.workflows_blocks.blocks import WorkflowBlock
-
-
-def _get_workflow_nodes(component_id):
-    return writer.core.base_component_tree.get_descendents(component_id)
-
-def run_workflow_by_key(session, workflow_key: str, execution_env: Dict):
-    all_components = writer.core.base_component_tree.components.values()
-    workflows = list(filter(lambda c: c.type == "workflows_workflow" and c.content.get("key") == workflow_key, all_components))
-    if len(workflows) == 0:
-        return
-    workflow = workflows[0]
-
-    return run_workflow(session, workflow.id, execution_env)
-
-
-def run_workflow(session, component_id: str, execution_env: Dict):
-    execution: Dict[str, WorkflowBlock] = {}
-    nodes = _get_workflow_nodes(component_id)
-    return_value = None
-    try:
-        for node in get_terminal_nodes(nodes):
-            run_node(node, nodes, execution, session, execution_env)
-        for component_id, tool in execution.items():
-            if tool and tool.return_value is not None:
-                return_value = tool.return_value
-    except BaseException as e:
-        _generate_run_log(session, execution, "Failed workflow execution", "error")
-        raise e
-    else:
-        _generate_run_log(session, execution, "Workflow execution", "info", return_value)
-    return return_value
-
-def _generate_run_log(session: "writer.core.WriterSession", execution: Dict[str, WorkflowBlock], title: str, entry_type: Literal["info", "error"], return_value: Optional[Any] = None):
-    if not writer.core.Config.is_mail_enabled_for_log:
-        return
-    exec_log:WorkflowExecutionLog = WorkflowExecutionLog(summary=[])
-    for component_id, tool in execution.items():
-        exec_log.summary.append({
-            "componentId": component_id,
-            "outcome": tool.outcome,
-            "result": tool.result,
-            "returnValue": tool.return_value,
-            "executionEnvironment": tool.execution_env,
-            "executionTimeInSeconds": tool.execution_time_in_seconds 
-        })
-    msg = "Execution finished."
-    state = session.session_state
-    state.add_log_entry(entry_type, title, msg, workflow_execution=exec_log)
-
-
-def get_terminal_nodes(nodes):
-    return [node for node in nodes if not node.outs]
-
-def _get_node_dependencies(target_node: "Component", nodes: List["Component"]):
-    dependencies:List[Tuple] = []
-    parent_id = target_node.parentId
-    if not parent_id:
-        return []
-    for node in nodes:
-        if not node.outs:
-            continue
-        for out in node.outs:
-            to_node_id = out.get("toNodeId")
-            out_id = out.get("outId")
-            if to_node_id == target_node.id:
-                dependencies.append((node, out_id))
-    return dependencies
-    
-
-def get_branch_nodes(root_node_id: str):
-    root_node = writer.core.base_component_tree.get_component(root_node_id)
-    if not root_node:
-        return []
-    branch_nodes = [root_node]
-    if not root_node.outs:
+import writer.core_ui
+from writer.ss_types import WorkflowExecutionLog, WriterConfigurationError
+
+
+class WorkflowRunner():
+
+    def __init__(self, session: writer.core.WriterSession):
+        self.session = session
+
+    def run_workflow_by_key(self, workflow_key: str, execution_environment: Dict = {}):
+        all_components = self.session.session_component_tree.components.values()
+        workflows = list(filter(lambda c: c.type == "workflows_workflow" and c.content.get("key") == workflow_key, all_components))
+        if len(workflows) == 0:
+            raise ValueError(f'Workflow with key "{workflow_key}" not found.')
+        workflow = workflows[0]
+        return self.run_workflow(workflow.id, execution_environment, f"Workflow execution ({workflow_key})")
+
+    def _get_workflow_nodes(self, component_id):
+        return self.session.session_component_tree.get_descendents(component_id)
+
+    def _get_branch_nodes(self, base_component_id: str, base_outcome: Optional[str]=None):
+        root_node = self.session.session_component_tree.get_component(base_component_id)
+        if not root_node:
+            raise RuntimeError(f'Cannot obtain branch. Could not find component "{base_component_id}".')
+        if not root_node:
+            return []
+        branch_nodes: List[writer.core_ui.Component] = []
+        if not root_node.outs:
+            return branch_nodes
+        for out in root_node.outs:
+            if base_outcome is not None and base_outcome != out.get("outId"):
+                continue
+            branch_root_node = self.session.session_component_tree.get_component(out.get("toNodeId"))
+            if not branch_root_node:
+                continue
+            branch_nodes.append(branch_root_node)
+            branch_nodes += self._get_branch_nodes(out.get("toNodeId"), base_outcome=None)
         return branch_nodes
-    for out in root_node.outs:
-        branch_nodes += get_branch_nodes(out.get("toNodeId"))
-    return branch_nodes
 
-
-def _is_outcome_managed(target_node: "Component", target_out_id: str):
-    if not target_node.outs:
+    def run_branch(self, base_component_id: str, base_outcome: str, execution_environment: Dict, title: str = "Branch execution"):
+        nodes = self._get_branch_nodes(base_component_id, base_outcome)
+        return self.run_nodes(nodes, execution_environment, title)
+
+    def run_workflow(self, component_id: str, execution_environment: Dict, title="Workflow execution"):
+        nodes = self._get_workflow_nodes(component_id)
+        return self.run_nodes(nodes, execution_environment, title)
+
+    def run_nodes(self, nodes: List[writer.core_ui.Component], execution_environment: Dict, title: str = "Workflow execution"):
+        execution: Dict[str, writer.blocks.base_block.WorkflowBlock] = {}
+        return_value = None
+        try:
+            for node in self.get_terminal_nodes(nodes):
+                self.run_node(node, nodes, execution_environment, execution)
+            for tool in execution.values():
+                if tool and tool.return_value is not None:
+                    return_value = tool.return_value
+        except WriterConfigurationError:
+            self._generate_run_log(execution, title, "error")
+            # No need to re-raise, it's a configuration error under control and shown as message in the relevant tool
+        except BaseException as e:
+            self._generate_run_log(execution, title, "error")
+            raise e
+        else:
+            self._generate_run_log(execution, title, "info", return_value)
+        return return_value
+
+    def _summarize_data_for_log(self, data):
+        if isinstance(data, list):
+            return [self._summarize_data_for_log(item) for item in data]
+        if isinstance(data, dict):
+            return {k : self._summarize_data_for_log(v) for k, v in data.items()}
+        if isinstance(data, (str, int, float, bool, type(None))):
+            return data
+        try:
+            return json.loads(json.dumps(data))
+        except (TypeError, OverflowError):
+            return f"Can't be displayed in the log. Value of type: {str(type(data))}."
+
+
+    def _generate_run_log(self,
+                          execution: Dict[str, writer.blocks.base_block.WorkflowBlock],
+                          title: str,
+                          entry_type: Literal["info", "error"],
+                          return_value: Optional[Any] = None):
+        if not writer.core.Config.is_mail_enabled_for_log:
+            return
+        exec_log:WorkflowExecutionLog = WorkflowExecutionLog(summary=[])
+        for component_id, tool in execution.items():
+            exec_log.summary.append({
+                "componentId": component_id,
+                "outcome": tool.outcome,
+                "message": tool.message,
+                "result": self._summarize_data_for_log(tool.result),
+                "returnValue": self._summarize_data_for_log(tool.return_value),
+                "executionEnvironment": self._summarize_data_for_log(tool.execution_environment),
+                "executionTimeInSeconds": tool.execution_time_in_seconds 
+            })
+        msg = "Execution finished."
+        
+        self.session.session_state.add_log_entry(entry_type, title, msg, workflow_execution=exec_log)
+
+
+    def get_terminal_nodes(self, nodes):
+        return [node for node in nodes if not node.outs]
+
+    def _get_node_dependencies(self, target_node: writer.core_ui.Component, nodes: List[writer.core_ui.Component]):
+        dependencies:List[Tuple] = []
+        parent_id = target_node.parentId
+        if not parent_id:
+            return []
+        for node in nodes:
+            if not node.outs:
+                continue
+            for out in node.outs:
+                to_node_id = out.get("toNodeId")
+                out_id = out.get("outId")
+                if to_node_id == target_node.id:
+                    dependencies.append((node, out_id))
+        return dependencies
+
+    def _is_outcome_managed(self, target_node: writer.core_ui.Component, target_out_id: str):
+        if not target_node.outs:
+            return False
+        for out in target_node.outs:
+            if out.get("outId") == target_out_id:
+                return True
         return False
-    for out in target_node.outs:
-        if out.get("outId") == target_out_id:
-            return True
-    return False
-
-
-def run_node(target_node: "Component", nodes: List["Component"], execution: Dict, session: "writer.core.WriterSession", execution_env: Dict):
-    tool_class = writer.workflows_blocks.blocks.block_map.get(target_node.type)
-    if not tool_class:
-        raise RuntimeError(f"Couldn't find tool for {target_node.type}.")
-    dependencies = _get_node_dependencies(target_node, nodes)
-
-    tool = execution.get(target_node.id)
-    if tool:
-        return tool
-
-    result = None
-    matched_dependencies = 0
-    for node, out_id in dependencies:
-        tool = run_node(node, nodes, execution, session, execution_env)
-        if not tool:
-            continue
-        if tool.outcome == out_id:
-            matched_dependencies += 1
-        result = tool.result
-        if tool.return_value is not None:
+
+    def run_node(self, target_node: writer.core_ui.Component, nodes: List[writer.core_ui.Component], execution_environment: Dict, execution: Dict[str, writer.blocks.base_block.WorkflowBlock]):
+        tool_class = writer.blocks.base_block.block_map.get(target_node.type)
+        if not tool_class:
+            raise RuntimeError(f'Could not find tool for "{target_node.type}".')
+        dependencies = self._get_node_dependencies(target_node, nodes)
+
+        tool = execution.get(target_node.id)
+        if tool:
+            return tool
+
+        result = None
+        matched_dependencies = 0
+        for node, out_id in dependencies:
+            tool = self.run_node(node, nodes, execution_environment, execution)
+            if not tool:
+                continue
+            if tool.outcome == out_id:
+                matched_dependencies += 1
+            result = tool.result
+            if tool.return_value is not None:
+                return
+
+        if len(dependencies) > 0 and matched_dependencies == 0:
             return
 
-    if len(dependencies) > 0 and matched_dependencies == 0:
-        return
-
-    results = {
-        "result": result,
-        "results": { k:v.result for k,v in execution.items() }
-    }
-    tool = tool_class(target_node, execution, session, execution_env | results)
-    
-    try:
-        start_time = time.time()
-        tool.run()
-        tool.execution_time_in_seconds = time.time() - start_time
-    except BaseException as e:
-        if tool and not tool.result:
-            tool.result = repr(e)
-        if not tool.outcome or not _is_outcome_managed(target_node, tool.outcome):
-            raise e
-    finally:
-        execution[target_node.id] = tool
-    
-    return tool
\ No newline at end of file
+        expanded_execution_environment = execution_environment | {
+            "result": result,
+            "results": { k:v.result for k,v in execution.items() }
+        }
+        tool = tool_class(target_node.id, self, expanded_execution_environment)
+        
+        try:
+            start_time = time.time()
+            tool.run()
+            tool.execution_time_in_seconds = time.time() - start_time
+        except BaseException as e:
+            if not tool:
+                raise e
+            if not tool.outcome:
+                tool.outcome = "error"
+            if isinstance(e, WriterConfigurationError):
+                tool.message = str(e)
+            if not tool.outcome or not self._is_outcome_managed(target_node, tool.outcome):
+                raise e
+        finally:
+            execution[target_node.id] = tool
+        
+        return tool
\ No newline at end of file
diff --git a/src/writer/workflows_blocks/__init__.py b/src/writer/workflows_blocks/__init__.py
deleted file mode 100644
index b6f73b483..000000000
--- a/src/writer/workflows_blocks/__init__.py
+++ /dev/null
@@ -1,31 +0,0 @@
-from writer.workflows_blocks.addtostatelist import AddToStateList
-from writer.workflows_blocks.calleventhandler import CallEventHandler
-from writer.workflows_blocks.foreach import ForEach
-from writer.workflows_blocks.httprequest import HTTPRequest
-from writer.workflows_blocks.logmessage import LogMessage
-from writer.workflows_blocks.parsejson import ParseJSON
-from writer.workflows_blocks.returnvalue import ReturnValue
-from writer.workflows_blocks.runworkflow import RunWorkflow
-from writer.workflows_blocks.setstate import SetState
-from writer.workflows_blocks.writeraddchatmessage import WriterAddChatMessage
-from writer.workflows_blocks.writerchat import WriterChat
-from writer.workflows_blocks.writerclassification import WriterClassification
-from writer.workflows_blocks.writercompletion import WriterCompletion
-from writer.workflows_blocks.writerinitchat import WriterInitChat
-from writer.workflows_blocks.writernocodeapp import WriterNoCodeApp
-
-SetState.register("workflows_setstate")
-WriterClassification.register("workflows_writerclassification")
-WriterCompletion.register("workflows_writercompletion")
-HTTPRequest.register("workflows_httprequest")
-RunWorkflow.register("workflows_runworkflow")
-WriterNoCodeApp.register("workflows_writernocodeapp")
-ForEach.register("workflows_foreach")
-LogMessage.register("workflows_logmessage")
-WriterChat.register("workflows_writerchat")
-WriterAddChatMessage.register("workflows_writeraddchatmessage")
-ParseJSON.register("workflows_parsejson")
-CallEventHandler.register("workflows_calleventhandler")
-AddToStateList.register("workflows_addtostatelist")
-ReturnValue.register("workflows_returnvalue")
-WriterInitChat.register("workflows_writerinitchat")
\ No newline at end of file
diff --git a/src/writer/workflows_blocks/blocks.py b/src/writer/workflows_blocks/blocks.py
deleted file mode 100644
index 3f7023d04..000000000
--- a/src/writer/workflows_blocks/blocks.py
+++ /dev/null
@@ -1,53 +0,0 @@
-from typing import Dict, List
-
-import writer.core
-import writer.core_ui
-import writer.workflows_blocks
-from writer.ss_types import InstancePath
-
-block_map = {}
-
-class WorkflowBlock:
-    
-    @classmethod
-    def register(cls, type: str):
-        block_map[type] = cls
-
-    def __init__(self, component: "writer.core_ui.Component", execution: Dict, session: "writer.core.WriterSession", execution_env: Dict):
-        self.outcome = None
-        self.component = component
-        self.execution = execution
-        self.execution_time_in_seconds = -1.0
-        self.session = session
-        self.execution_env = execution_env
-        self.result = None
-        self.return_value = None
-        self.evaluator = writer.core.Evaluator(session.session_state, session.session_component_tree)
-        self.instance_path: InstancePath = [{"componentId": self.component.id, "instanceNumber": 0}]
-
-    def _get_nodes_at_outcome(self, target_outcome: str):
-        outs = self.component.outs
-        nodes:List["writer.core_ui.Component"] = []
-        if not outs:
-            return nodes
-        for out in outs:
-            if out.get("outId") == target_outcome:
-                component_id = out.get("toNodeId")
-                component = writer.core.base_component_tree.get_component(component_id)
-                if not component:
-                    continue
-                nodes.append(component)
-        return nodes
-
-    def _get_field(self, field_key: str, as_json=False, default_field_value=None):
-        if default_field_value is None:
-            if as_json:
-                default_field_value = "{}"
-            else:
-                default_field_value = ""
-        v = self.evaluator.evaluate_field(self.instance_path, field_key, base_context=self.execution_env, as_json=as_json, default_field_value=default_field_value)
-
-        return v
-
-    def run(self):
-        pass
\ No newline at end of file
diff --git a/tests/backend/blocks/conftest.py b/tests/backend/blocks/conftest.py
new file mode 100644
index 000000000..d41f61e6f
--- /dev/null
+++ b/tests/backend/blocks/conftest.py
@@ -0,0 +1,52 @@
+from typing import Dict
+
+import pytest
+from writer.core import WriterSession, WriterState
+from writer.core_ui import Branch, Component, ComponentTree, ComponentTreeBranch
+from writer.workflows import WorkflowRunner
+
+
+class BlockTesterMockSession(WriterSession):
+
+    def __init__(self):
+        self.session_state = WriterState({})
+        self.bmc_branch = ComponentTreeBranch(Branch.bmc)
+        component_tree = ComponentTree([self.bmc_branch])
+        self.session_component_tree = component_tree
+
+    def add_fake_component(self, content={}, id="fake_id", type="fake_type"):
+        self.bmc_branch.attach(Component(id=id, type=type, content=content))
+
+
+class BlockTesterMockWorkflowRunner(WorkflowRunner):
+
+    def __init__(self, session):
+        super().__init__(session)
+
+    def run_branch(self, component_id: str, base_outcome_id: str, execution_environment: Dict, title: str):
+        return f"Branch run {component_id} {base_outcome_id}"
+
+    def run_workflow_by_key(self, workflow_key: str, execution_environment: Dict):
+        if "env_injection_test" in execution_environment:
+            return execution_environment.get("env_injection_test")
+        if workflow_key == "workflow1":
+            return 1
+        if workflow_key == "workflowDict":
+            return { "a": "b" }
+        if workflow_key == "duplicator":
+            return execution_environment.get("item") * 2
+        if workflow_key == "showId":
+            return execution_environment.get("itemId")
+        if workflow_key == "boom":
+            return 1/0
+        raise ValueError("Workflow not found.")
+
+
+@pytest.fixture
+def session():
+    yield BlockTesterMockSession()
+
+
+@pytest.fixture
+def runner(session):
+    yield BlockTesterMockWorkflowRunner(session)
diff --git a/tests/backend/blocks/test_addtostatelist.py b/tests/backend/blocks/test_addtostatelist.py
new file mode 100644
index 000000000..ffc222548
--- /dev/null
+++ b/tests/backend/blocks/test_addtostatelist.py
@@ -0,0 +1,37 @@
+import pytest
+from writer.blocks.addtostatelist import AddToStateList
+from writer.workflows import WorkflowRunner
+
+
+def test_empty_list(session, runner):
+    session.add_fake_component({
+        "element": "my_list",
+        "value": "my_value"
+    })
+    block = AddToStateList("fake_id", runner, {})
+    block.run()
+    assert block.outcome == "success"
+    assert session.session_state["my_list"] == ["my_value"]
+
+def test_non_empty_list(session, runner):
+    session.session_state["my_list"] = ["a"]
+    session.add_fake_component({
+        "element": "my_list",
+        "value": "b"
+    })
+    block = AddToStateList("fake_id", runner, {})
+    block.run()
+    assert block.outcome == "success"
+    assert session.session_state["my_list"] == ["a", "b"]
+
+
+def test_non_list_element(session, runner):
+    session.session_state["my_element"] = "dog"
+    session.add_fake_component({
+        "element": "my_element",
+        "value": "cat"
+    })
+    block = AddToStateList("fake_id", runner, {})
+    with pytest.raises(ValueError):
+        block.run()
+    assert block.outcome == "error"
\ No newline at end of file
diff --git a/tests/backend/blocks/test_base_block.py b/tests/backend/blocks/test_base_block.py
new file mode 100644
index 000000000..b044e7c93
--- /dev/null
+++ b/tests/backend/blocks/test_base_block.py
@@ -0,0 +1,44 @@
+from writer.blocks.base_block import WorkflowBlock
+from writer.core import WriterState
+
+
+def test_get_field(session, runner):
+    session.session_state = WriterState({
+        "animal": "rat",
+        "my_list": "[1,2,3]",
+        "my_dict": '{ "a": "b" }'
+    })
+    session.add_fake_component({
+        "my_element": "@{animal}",
+        "my_list": "@{my_list}",
+        "my_dict": "@{my_dict}"
+    })
+    block = WorkflowBlock("fake_id", runner, {})
+    assert "rat" == block._get_field("my_element", as_json=False, default_field_value="elephant")
+    assert [1, 2, 3] == block._get_field("my_list", as_json=True, default_field_value=None)
+    assert "b" == block._get_field("my_dict", as_json=True, default_field_value=None).get("a")
+    assert "ok" == block._get_field("ghost_field", as_json=False, default_field_value="ok")
+    assert {} == block._get_field("ghost_field", as_json=True)
+    assert "ok" == block._get_field("ghost_field_json", as_json=True, default_field_value='{ "ok": "ok" }').get("ok")
+    block.run()
+    assert block.outcome is None
+
+
+def test_set_state(session, runner):
+    session.session_state = WriterState({
+        "animal": "rat",
+        "my_list": [1,2,4],
+        "my_dict": { "animal": "dog"},
+        "unchanged": "unchanged"
+    })
+    block = WorkflowBlock("fake_id", runner, {})
+    block._set_state("animal", "cat")
+    block._set_state("animal", "bat")
+    block._set_state("my_list", [1, 2])
+    block._set_state("my_dict", { "animal": "cat"})
+    block.run()
+    assert session.session_state["animal"] == "bat"
+    assert session.session_state["my_list"] == [1, 2]
+    assert session.session_state["my_dict"]["animal"] == "cat"
+    assert session.session_state["unchanged"] == "unchanged"
+    assert block.outcome is None
\ No newline at end of file
diff --git a/tests/backend/blocks/test_calleventhandler.py b/tests/backend/blocks/test_calleventhandler.py
new file mode 100644
index 000000000..726418fb8
--- /dev/null
+++ b/tests/backend/blocks/test_calleventhandler.py
@@ -0,0 +1,48 @@
+import pytest
+import writer.core
+from writer.blocks.calleventhandler import CallEventHandler
+
+
+def valid_handler(state):
+    state["animal"] = "duck"
+    return 1
+
+def invalid_handler(state):
+    state["animal"] = "cat"
+    return 1/0
+
+class MockHandlerRegistry():
+
+    def find_handler_callable(self, handler_name: str):
+        if handler_name == "valid_handler":
+            return valid_handler
+        elif handler_name == "invalid_handler":
+            return invalid_handler
+        raise None
+
+class MockAppProcess():
+    
+    def __init__(self):
+        self.handler_registry = MockHandlerRegistry()
+
+def test_call_event_handler(session, runner):
+    writer.core.get_app_process = lambda: MockAppProcess()
+    session.add_fake_component({
+        "name": "valid_handler"
+    })
+    block = CallEventHandler("fake_id", runner, {})
+    block.run()
+    assert block.outcome == "success"
+    assert block.result == 1
+    assert session.session_state["animal"] == "duck"
+
+def test_invalid_json(session, runner):
+    writer.core.get_app_process = lambda: MockAppProcess()
+    session.add_fake_component({
+        "name": "invalid_handler"
+    })
+    block = CallEventHandler("fake_id", runner, {})
+    with pytest.raises(BaseException):
+        block.run()
+    assert block.outcome == "error"
+    assert session.session_state["animal"] == "cat"
\ No newline at end of file
diff --git a/tests/backend/blocks/test_foreach.py b/tests/backend/blocks/test_foreach.py
new file mode 100644
index 000000000..2377959f2
--- /dev/null
+++ b/tests/backend/blocks/test_foreach.py
@@ -0,0 +1,53 @@
+import pytest
+from writer.blocks.foreach import ForEach
+
+
+def test_basic_list(session, runner):
+    session.add_fake_component({
+        "workflowKey": "workflow1",
+        "items": "[2, 2, 2, 2]"
+    })
+    block = ForEach("fake_id", runner, {})
+    block.run()
+    assert block.outcome == "success"
+    assert block.result == [1, 1, 1, 1]
+
+def test_list_of_dict(session, runner):
+    session.add_fake_component({
+        "workflowKey": "workflowDict",
+        "items": "[2, 2]"
+    })
+    block = ForEach("fake_id", runner, {})
+    block.run()
+    assert block.outcome == "success"
+    assert block.result == [{"a": "b"}, {"a": "b"}]
+
+def test_basic_dict(session, runner):
+    session.add_fake_component({
+        "workflowKey": "workflow1",
+        "items": '{"a": "zzz", "b": "zzz"}'
+    })
+    block = ForEach("fake_id", runner, {})
+    block.run()
+    assert block.outcome == "success"
+    assert block.result == {"a": 1, "b": 1}
+
+def test_workflow_that_does_not_exist(session, runner):
+    session.add_fake_component({
+        "workflowKey": "workflowThatDoesNotExist",
+        "items": '{"a": "zzz", "b": "zzz"}'
+    })
+    block = ForEach("fake_id", runner, {})
+    with pytest.raises(ValueError):
+        block.run()
+    assert block.outcome == "error"
+
+def test_duplicator(session, runner):
+    session.add_fake_component({
+        "workflowKey": "duplicator",
+        "items": '{"a": 1, "b": 2, "c": 11}'
+    })
+    block = ForEach("fake_id", runner, {})
+    block.run()
+    assert block.outcome == "success"
+    assert block.result == {"a": 2, "b": 4, "c": 22}
\ No newline at end of file
diff --git a/tests/backend/blocks/test_httprequest.py b/tests/backend/blocks/test_httprequest.py
new file mode 100644
index 000000000..3d3388ff0
--- /dev/null
+++ b/tests/backend/blocks/test_httprequest.py
@@ -0,0 +1,121 @@
+import json
+
+import pytest
+import requests
+from writer.blocks.httprequest import HTTPRequest
+
+
+class FakeResponse():
+    def __init__(self, status_code=200, ok=True, headers={}, text=None):
+        self.status_code = status_code
+        self.ok = ok
+        self.headers = headers
+        self.text = text
+        self.json = lambda: json.loads(text)
+
+
+def fake_request(method, url, headers={}, data=""):
+    if not headers.get("TestHeader", "not-a-sec-ret"):
+        raise RuntimeError("Test header not present.")
+    if method == "GET" and url == "https://www.duck.com":
+        return FakeResponse(
+            headers={"Content-Type": "text/plain"},
+            text="Ducks are birds."
+        )
+    if method == "POST" and url == "https://www.elephant.com":
+        return FakeResponse(
+            headers={"Content-Type": "application/json"},
+            text='{ "elephant_name": "Momo", "request_body": "' + data + '" }'
+        )
+    if method == "POST" and url == "https://www.elephant.com/history":
+        return FakeResponse(
+            status_code=404,
+            ok=False,
+            headers={"Content-Type": "application/json"},
+            text='{ "error_message": "Page not found." }'
+        )
+
+    raise requests.ConnectionError()
+
+
+@pytest.mark.explicit
+def test_actual_request(session, runner):
+    session.add_fake_component({
+        "url": 'https://www.example.com'
+    })
+    block = HTTPRequest("fake_id", runner, {})
+    block.run()
+    assert block.outcome == "success"
+    assert block.result.get("headers") is not None
+
+
+@pytest.mark.explicit
+def test_actual_failing_request(session, runner):
+    session.add_fake_component({
+        "url": 'https://www.site-that-does-not-exist-3017673369.com'
+    })
+    block = HTTPRequest("fake_id", runner, {})
+    with pytest.raises(requests.ConnectionError):
+        block.run()
+    assert block.outcome == "connectionError"
+
+
+@pytest.mark.explicit
+def test_actual_request_with_bad_path(session, runner):
+    session.add_fake_component({
+        "url": 'https://www.writer.com/3017673369'
+    })
+    block = HTTPRequest("fake_id", runner, {})
+    with pytest.raises(RuntimeError):
+        block.run()
+    assert block.outcome == "responseError"
+
+
+def test_patched_request(session, runner):
+    requests.request = fake_request
+    session.add_fake_component({
+        "url": "https://www.duck.com"
+    })
+    block = HTTPRequest("fake_id", runner, {})
+    block.run()
+    assert block.outcome == "success"
+    assert block.result.get("body") == "Ducks are birds."
+
+
+def test_patched_request_to_nowhere(session, runner):
+    requests.request = fake_request
+    session.add_fake_component({
+        "url": "https://www.cat.com"
+    })
+    block = HTTPRequest("fake_id", runner, {})
+    with pytest.raises(requests.ConnectionError):
+        block.run()
+    assert block.outcome == "connectionError"
+
+
+def test_patched_request_with_json(session, runner):
+    requests.request = fake_request
+    session.add_fake_component({
+        "url": "https://www.elephant.com",
+        "method": "POST",
+        "body": "Posting the elephant."
+    })
+    block = HTTPRequest("fake_id", runner, {})
+    block.run()
+    assert block.outcome == "success"
+    assert block.result.get("body").get("elephant_name") == "Momo"
+    assert block.result.get("body").get("request_body") == "Posting the elephant."
+
+
+def test_patched_request_with_json_and_bad_path(session, runner):
+    requests.request = fake_request
+    session.add_fake_component({
+        "url": "https://www.elephant.com/history",
+        "method": "POST",
+        "body": "Posting the elephant."
+    })
+    block = HTTPRequest("fake_id", runner, {})
+    with pytest.raises(RuntimeError):
+        block.run()
+    assert block.outcome == "responseError" # due to not "ok"
+    assert block.result.get("body").get("error_message") == "Page not found."
diff --git a/tests/backend/blocks/test_logmessage.py b/tests/backend/blocks/test_logmessage.py
new file mode 100644
index 000000000..76f1b90cd
--- /dev/null
+++ b/tests/backend/blocks/test_logmessage.py
@@ -0,0 +1,73 @@
+import pytest
+import writer.core
+from writer.blocks.logmessage import LogMessage
+from writer.core import WriterState
+
+
+def test_log_message(session, runner):
+    session.session_state = WriterState({
+        "animal": "rat",
+    }, [{"type": "test", "payload": "Just a test"}])
+    session.add_fake_component({
+        "message": "The quick brown fox is under the table."
+    })
+    writer.core.Config.is_mail_enabled_for_log = True
+    block = LogMessage("fake_id", runner, {})
+    block.run()
+    assert block.outcome == "success"
+    latest_mail = session.session_state.mail[0]
+    assert latest_mail.get("type") == "logEntry"
+    assert latest_mail.get("payload").get("type") == "info"
+    assert latest_mail.get("payload").get("message") == "The quick brown fox is under the table."
+
+
+def test_log_message_with_template(session, runner):
+    session.session_state = WriterState({
+        "animal": "rat",
+    })
+    session.add_fake_component({
+        "message": "The quick brown @{animal} is under the @{object}."
+    })
+    writer.core.Config.is_mail_enabled_for_log = True
+    block = LogMessage("fake_id", runner, {
+        "object": "tent"
+    })
+    block.run()
+    assert block.outcome == "success"
+    latest_mail = session.session_state.mail[0]
+    assert latest_mail.get("type") == "logEntry"
+    assert latest_mail.get("payload").get("type") == "info"
+    assert latest_mail.get("payload").get("message") == "The quick brown rat is under the tent."
+
+
+def test_log_error_message(session, runner):
+    session.session_state = WriterState({
+        "animal": "squirrel",
+    })
+    session.add_fake_component({
+        "type": "error",
+        "message": "The quick brown @{animal} has escaped."
+    })
+    writer.core.Config.is_mail_enabled_for_log = True
+    block = LogMessage("fake_id", runner, {})
+    block.run()
+    assert block.outcome == "success"
+    latest_mail = session.session_state.mail[0]
+    assert latest_mail.get("type") == "logEntry"
+    assert latest_mail.get("payload").get("type") == "error"
+    assert latest_mail.get("payload").get("message") == "The quick brown squirrel has escaped."
+
+
+def test_empty_message(session, runner):
+    session.session_state = WriterState({
+        "animal": None,
+    })
+    session.add_fake_component({
+        "type": "error",
+        "message": "@{animals}"
+    })
+    writer.core.Config.is_mail_enabled_for_log = True
+    block = LogMessage("fake_id", runner, {})
+    with pytest.raises(ValueError):
+        block.run()
+    assert block.outcome == "error"
\ No newline at end of file
diff --git a/tests/backend/blocks/test_parsejson.py b/tests/backend/blocks/test_parsejson.py
new file mode 100644
index 000000000..ae13f0bd9
--- /dev/null
+++ b/tests/backend/blocks/test_parsejson.py
@@ -0,0 +1,25 @@
+import json
+
+import pytest
+from writer.blocks.parsejson import ParseJSON
+from writer.workflows import WorkflowRunner
+
+
+def test_valid_json(session, runner):
+    session.add_fake_component({
+        "plainText": '{ "hi": "yes" }'
+    })
+    block = ParseJSON("fake_id", runner, {})
+    block.run()
+    assert block.outcome == "success"
+    assert block.result.get("hi") == "yes"
+
+def test_invalid_json(session, runner):
+    session.add_fake_component({
+        "plainText": '{ "hi": yes }'
+    })
+    block = ParseJSON("fake_id", runner, {})
+    with pytest.raises(json.JSONDecodeError):
+        block.run()
+
+    assert block.outcome == "error"
\ No newline at end of file
diff --git a/tests/backend/blocks/test_returnvalue.py b/tests/backend/blocks/test_returnvalue.py
new file mode 100644
index 000000000..13d3427cc
--- /dev/null
+++ b/tests/backend/blocks/test_returnvalue.py
@@ -0,0 +1,30 @@
+import pytest
+from writer.blocks.returnvalue import ReturnValue
+from writer.core import WriterState
+
+
+def test_basic_return(session, runner):
+    session.session_state = WriterState({
+        "animal": "marmot",
+    })
+    session.add_fake_component({
+        "value": "@{animal}"
+    })
+    block = ReturnValue("fake_id", runner, {})
+    block.run()
+    assert block.outcome == "success"    
+    assert block.result == block.return_value
+    assert block.return_value == "marmot"
+
+def test_empty_return(session, runner):
+    session.session_state = WriterState({
+        "animal": None,
+    })
+    session.add_fake_component({
+        "value": "@{animal}"
+    })
+    block = ReturnValue("fake_id", runner, {})
+    
+    with pytest.raises(ValueError):
+        block.run()
+    assert block.outcome == "error"
\ No newline at end of file
diff --git a/tests/backend/blocks/test_runworkflow.py b/tests/backend/blocks/test_runworkflow.py
new file mode 100644
index 000000000..2e3a0d90d
--- /dev/null
+++ b/tests/backend/blocks/test_runworkflow.py
@@ -0,0 +1,31 @@
+import pytest
+from writer.blocks.runworkflow import RunWorkflow
+
+
+def test_workflow_that_does_not_exist(session, runner):
+    session.add_fake_component({
+        "workflowKey": "workflowThatDoesNotExist",
+    })
+    block = RunWorkflow("fake_id", runner, {})
+    with pytest.raises(ValueError):
+        block.run()
+    assert block.outcome == "error"
+
+def test_duplicator(session, runner):
+    session.add_fake_component({
+        "workflowKey": "duplicator",
+        "executionEnv": '{"item": 23}'
+    })
+    block = RunWorkflow("fake_id", runner, {})
+    block.run()
+    assert block.outcome == "success"
+    assert block.result == 46
+
+def test_bad_workflow(session, runner):
+    session.add_fake_component({
+        "workflowKey": "boom"
+    })
+    block = RunWorkflow("fake_id", runner, {})
+    with pytest.raises(BaseException):
+        block.run()
+    assert block.outcome == "error"
\ No newline at end of file
diff --git a/tests/backend/blocks/test_setstate.py b/tests/backend/blocks/test_setstate.py
new file mode 100644
index 000000000..82bfbdee3
--- /dev/null
+++ b/tests/backend/blocks/test_setstate.py
@@ -0,0 +1,61 @@
+import pytest
+from writer.blocks.setstate import SetState
+from writer.workflows import WorkflowRunner
+
+
+def test_basic_assignment(session):
+    session.add_fake_component({
+        "element": "my_element",
+        "value": "my_value"
+    })
+    runner = WorkflowRunner(session)
+    block = SetState("fake_id", runner, {})
+    block.run()
+    assert block.outcome == "success"
+    assert session.session_state["my_element"] == "my_value"
+
+def test_nested_assignment_without_parent(session):
+    session.add_fake_component({
+        "element": "parent_element.my_element",
+        "value": "my_value"
+    })
+    runner = WorkflowRunner(session)
+    block = SetState("fake_id", runner, {})
+    with pytest.raises(ValueError):
+        block.run()
+    assert block.outcome == "error"
+
+def test_nested_assignment_with_parent(session, runner):
+    session.session_state["parent_element"] = {
+        "sibling_element": "yes"
+    }
+    session.add_fake_component({
+        "element": "parent_element.my_element",
+        "value": "my_value"
+    })
+    block = SetState("fake_id", runner, {})
+    block.run()
+    assert block.outcome == "success"
+    assert session.session_state["parent_element"]["sibling_element"] == "yes"
+    assert session.session_state["parent_element"]["my_element"] == "my_value"
+
+def test_assignment_with_empty_element(session):
+    session.add_fake_component({
+        "element": "",
+        "value": "my_value"
+    })
+    runner = WorkflowRunner(session)
+    block = SetState("fake_id", runner, {})
+    with pytest.raises(ValueError):
+        block.run()
+    assert block.outcome == "error"
+
+def test_assignment_with_empty_value(session):
+    session.add_fake_component({
+        "element": "my_element",
+        "value": ""
+    })
+    runner = WorkflowRunner(session)
+    block = SetState("fake_id", runner, {})
+    block.run()
+    assert block.outcome == "success"
\ No newline at end of file
diff --git a/tests/backend/blocks/test_writeraddchatmessage.py b/tests/backend/blocks/test_writeraddchatmessage.py
new file mode 100644
index 000000000..34a9db987
--- /dev/null
+++ b/tests/backend/blocks/test_writeraddchatmessage.py
@@ -0,0 +1,50 @@
+import pytest
+import writer.ai
+from writer.blocks.writeraddchatmessage import WriterAddChatMessage
+
+
+def test_add_chat_message(session, runner):
+    session.session_state["convo"] = writer.ai.Conversation()
+    session.add_fake_component({
+        "conversationStateElement": "convo",
+        "message": '{ "role": "user", "content": "hi" }'
+    })
+    block = WriterAddChatMessage("fake_id", runner, {})
+    assert len(session.session_state["convo"].messages) == 0
+    block.run()
+    assert len(session.session_state["convo"].messages) == 1
+
+
+def test_add_chat_message_bad_template(session, runner):
+    session.session_state["convo"] = writer.ai.Conversation()
+    session.add_fake_component({
+        "conversationStateElement": "@{convo}", # Should be convo not @{convo}
+        "message": '{ "role": "user", "content": "hi" }'
+    })
+    block = WriterAddChatMessage("fake_id", runner, {})
+    with pytest.raises(ValueError):
+        block.run()
+
+
+def test_add_chat_message_bad_message(session, runner):
+    session.session_state["convo"] = writer.ai.Conversation()
+    session.add_fake_component({
+        "conversationStateElement": "convo", # Should be convo not @{convo}
+        "message": '{ "x": "user", "content": "hi" }'
+    })
+    block = WriterAddChatMessage("fake_id", runner, {})
+    with pytest.raises(ValueError):
+        block.run()
+
+
+def test_add_chat_message_missing_convo(session, runner):
+    session.session_state["convo"] = None
+    session.add_fake_component({
+        "conversationStateElement": "@{convo}",
+        "message": '{ "role": "user", "content": "hi" }'
+    })
+    block = WriterAddChatMessage("fake_id", runner, {})
+    with pytest.raises(ValueError):
+        block.run()
+
+
diff --git a/tests/backend/blocks/test_writeraddtokg.py b/tests/backend/blocks/test_writeraddtokg.py
new file mode 100644
index 000000000..7042a874c
--- /dev/null
+++ b/tests/backend/blocks/test_writeraddtokg.py
@@ -0,0 +1,79 @@
+import pytest
+import writer.ai
+from writer.blocks.writeraddtokg import WriterAddToKG
+from writer.ss_types import WriterConfigurationError
+
+
+class MockFile():
+    pass
+
+class MockGraph():
+
+    def add_file(self, file):
+        assert isinstance(file, MockFile)
+
+def mock_retrieve_graph(graph_id):
+    assert graph_id == "abc123"
+    return MockGraph()
+
+def mock_upload_file(data, type, name):
+    assert data == b"123"
+    assert type == "application/pdf"
+    assert name == "interesting.pdf"
+    return MockFile()
+
+
+def test_add_to_kg(session, runner):
+    writer.ai.retrieve_graph = mock_retrieve_graph
+    writer.ai.upload_file = mock_upload_file
+    session.session_state["my_files"] = [
+        {
+            "data": b"123",
+            "type": "application/pdf",
+            "name": "interesting.pdf"
+        },
+        {
+            "data": b"123",
+            "type": "application/pdf",
+            "name": "interesting.pdf"
+        }
+    ]
+    session.add_fake_component({
+        "graphId": "abc123",
+        "files": "@{my_files}"
+    })
+    block = WriterAddToKG("fake_id", runner, {})
+    block.run()
+    assert block.outcome == "success"
+
+
+def test_add_to_kg_missing_type(session, runner):
+    writer.ai.retrieve_graph = mock_retrieve_graph
+    writer.ai.upload_file = mock_upload_file
+    session.session_state["my_files"] = [
+        {
+            "data": b"123",
+            "name": "interesting.pdf"
+        }
+    ]
+    session.add_fake_component({
+        "graphId": "abc123",
+        "files": "@{my_files}"
+    })
+    block = WriterAddToKG("fake_id", runner, {})
+    
+    with pytest.raises(WriterConfigurationError):
+        block.run()
+
+def test_add_to_kg_wrong_type(session, runner):
+    writer.ai.retrieve_graph = mock_retrieve_graph
+    writer.ai.upload_file = mock_upload_file
+    session.session_state["my_files"] = "should be list"
+    session.add_fake_component({
+        "graphId": "abc123",
+        "files": "@{my_files}"
+    })
+    block = WriterAddToKG("fake_id", runner, {})
+    
+    with pytest.raises(WriterConfigurationError):
+        block.run()
\ No newline at end of file
diff --git a/tests/backend/blocks/test_writerchat.py b/tests/backend/blocks/test_writerchat.py
new file mode 100644
index 000000000..661d8c2ea
--- /dev/null
+++ b/tests/backend/blocks/test_writerchat.py
@@ -0,0 +1,125 @@
+import json
+
+import pytest
+from writer.ai import Conversation
+from writer.blocks.writerchat import WriterChat
+
+
+class MockConversation(Conversation):
+
+    def __init__(self):
+        super().__init__()
+
+    def _check_tools(self, tools):
+        if tools is None or tools == []:
+            return
+        if len(tools) != 2:
+            raise RuntimeError("Invalid number of tools.")
+        function_tool = tools[0]
+        
+        assert function_tool.get("type") == "function"
+        assert function_tool.get("name") == "bat_locator"
+        assert function_tool.get("description") == "Locates bats."
+        assert function_tool.get("parameters").get("color") == {
+            "type": "string",
+            "description": "The color of the bat you're looking for."
+        }
+        graph_tool = tools[1]
+        assert graph_tool.get("type") == "graph"
+        assert graph_tool.get("graph_ids") == [111, 112, 113]
+
+    def complete(self, tools=None):
+        self._check_tools(tools)
+        return {
+            "role": "assistant",
+            "content": "Next to the grill."
+        }
+    
+    def stream_complete(self, tools=None):
+        self._check_tools(tools)
+        yield {
+            "role": "assistant",
+            "content": "On "
+        }
+        yield {
+            "role": "assistant",
+            "content": "the ",
+            "chunk": True
+        }
+        yield {
+            "role": "assistant",
+            "content": "car's ",
+            "chunk": True
+        }
+        yield {
+            "role": "assistant",
+            "content": "roof.",
+            "chunk": True
+        }
+
+@pytest.fixture
+def conversation():
+    return MockConversation()
+
+def test_chat_complete(session, runner, conversation):
+    conversation.add("user", "Hi, where's the bat?")
+    session.session_state["convo"] = conversation
+    session.add_fake_component({
+        "conversationStateElement": "convo",
+        "useStreaming": "no"
+    })
+    block = WriterChat("fake_id", runner, {})
+    block.run()
+    assert conversation.messages[1].get("content") == "Next to the grill."
+
+
+def test_chat_stream_complete(session, runner, conversation):
+    conversation.add("user", "Hi, where's the bat?")
+    session.session_state["convo"] = conversation
+    session.add_fake_component({
+        "conversationStateElement": "convo"
+        # streaming should be default
+    })
+    block = WriterChat("fake_id", runner, {})
+    block.run()
+    assert conversation.messages[1].get("content") == "On the car's roof."
+
+
+def test_chat_stream_complete_with_tools(session, runner, conversation):
+    conversation.add("user", "Hi, where's the bat?")
+    session.session_state["convo"] = conversation
+    session.add_fake_component({
+        "conversationStateElement": "convo",
+        "tools": json.dumps({
+            "bat_locator": {
+                "type": "function",
+                "description": "Locates bats.",
+                "parameters": {
+                    "color": {
+                        "type": "string",
+                        "description": "The color of the bat you're looking for."
+                    }
+                }
+            },
+            "known_bat_spots": {
+                "type": "graph",
+                "graph_ids": [111, 112, 113]
+            }
+        }),
+        "useStreaming": "yes"
+    })
+    block = WriterChat("fake_id", runner, {})
+    block.run()
+    assert conversation.messages[1].get("content") == "On the car's roof."
+
+
+def test_chat_stream_complete_no_conversation(session, runner, conversation):
+    conversation.add("user", "Hi, where's the bat?")
+    session.session_state["convo"] = "not_a_conversation"
+    session.add_fake_component({
+        "conversationStateElement": "convo"
+        # streaming should be default
+    })
+    block = WriterChat("fake_id", runner, {})
+    with pytest.raises(ValueError):
+        block.run()
\ No newline at end of file
diff --git a/tests/backend/blocks/test_writerclassification.py b/tests/backend/blocks/test_writerclassification.py
new file mode 100644
index 000000000..730968e77
--- /dev/null
+++ b/tests/backend/blocks/test_writerclassification.py
@@ -0,0 +1,42 @@
+import json
+
+import pytest
+import writer.ai
+from writer.blocks.writerclassification import WriterClassification
+
+
+def fake_complete(prompt, config):
+    additional_context = "It's about animal classification."
+    if "canine" in prompt and additional_context in prompt:
+        return "dog"
+    if "feline" in prompt and additional_context in prompt:
+        return "cat"
+    return "other"
+
+
+def test_classify(session, runner):
+    writer.ai.complete = fake_complete
+    session.add_fake_component({
+        "text": "canine",
+        "categories": json.dumps({
+            "cat": "Pertaining to cats.",
+            "dog": "Pertaining to dogs."
+        }),
+        "additionalContext": "It's about animal classification."
+    })
+    block = WriterClassification("fake_id", runner, {})
+    block.run()
+    assert block.result == "dog"
+    assert block.outcome == "category_dog"
+
+
+def test_classify_missing_categories(session, runner):
+    writer.ai.complete = fake_complete
+    session.add_fake_component({
+        "text": "canine",
+        "categories": json.dumps({})
+    })
+    block = WriterClassification("fake_id", runner, {})
+    
+    with pytest.raises(ValueError):
+        block.run()
\ No newline at end of file
diff --git a/tests/backend/blocks/test_writercompletion.py b/tests/backend/blocks/test_writercompletion.py
new file mode 100644
index 000000000..6573a7f8f
--- /dev/null
+++ b/tests/backend/blocks/test_writercompletion.py
@@ -0,0 +1,42 @@
+import writer.ai
+from writer.blocks.writercompletion import WriterCompletion
+
+
+def test_complete(session, runner):
+    def fake_complete(prompt, config):
+        assert config.get("temperature") == 0.9
+        assert config.get("model") == "buenos-aires-x-004"
+        assert prompt == "What color is the sea?"
+        return "Blue."
+
+    writer.ai.complete = fake_complete
+    session.add_fake_component({
+        "prompt": "What color is the sea?",
+        "modelId": "buenos-aires-x-004",
+        "temperature": "0.9"
+    })
+    block = WriterCompletion("fake_id", runner, {})
+    block.run()
+    assert block.result == "Blue."
+    assert block.outcome == "success"
+
+def test_complete_missing_text(session, runner):
+    def fake_complete(prompt, config):
+        assert config.get("temperature") == 0.9
+        assert config.get("model") == "buenos-aires-x-004"
+        assert not prompt
+        return "Plants are usually green."
+
+    writer.ai.complete = fake_complete
+    session.add_fake_component({
+        "prompt": "",
+        "modelId": "buenos-aires-x-004",
+        "temperature": "0.9"
+    })
+    block = WriterCompletion("fake_id", runner, {})
+ 
+    # Not expected to fail, just hallucinate
+
+    block.run()
+    assert block.result == "Plants are usually green."
+    assert block.outcome == "success"
\ No newline at end of file
diff --git a/tests/backend/blocks/test_writerinitchat.py b/tests/backend/blocks/test_writerinitchat.py
new file mode 100644
index 000000000..eb832cd73
--- /dev/null
+++ b/tests/backend/blocks/test_writerinitchat.py
@@ -0,0 +1,33 @@
+import pytest
+from writer.ai import Conversation
+from writer.blocks.writerinitchat import WriterInitChat
+
+
+def test_init_chat_already_initialized(session, runner):
+    session.session_state["convo"] = Conversation()
+    session.add_fake_component({
+        "conversationStateElement": "convo",
+    })
+    block = WriterInitChat("fake_id", runner, {})
+    block.run()
+    assert block.outcome == "success"
+
+
+def test_init_chat_already_initialized_with_rubbish(session, runner):
+    session.session_state["convo"] = "-hello -hello there. This is a conversation but not the right kind."
+    session.add_fake_component({
+        "conversationStateElement": "convo",
+    })
+    block = WriterInitChat("fake_id", runner, {})
+    
+    with pytest.raises(ValueError):
+        block.run()
+
+def test_init_chat_from_scratch(session, runner):
+    session.add_fake_component({
+        "conversationStateElement": "convo",
+    })
+    block = WriterInitChat("fake_id", runner, {})
+    block.run()
+    assert isinstance(session.session_state["convo"], Conversation)
+    assert block.outcome == "success"
\ No newline at end of file
diff --git a/tests/backend/blocks/test_writernocodeapp.py b/tests/backend/blocks/test_writernocodeapp.py
new file mode 100644
index 000000000..3ad96a75a
--- /dev/null
+++ b/tests/backend/blocks/test_writernocodeapp.py
@@ -0,0 +1,43 @@
+import json
+
+import pytest
+import writer.ai
+from writer.blocks.writernocodeapp import WriterNoCodeApp
+
+
+def fake_generate_content(application_id, app_inputs):
+    assert application_id == "123"
+
+    name = app_inputs.get("name")
+    animal = app_inputs.get("animal")
+
+    return f"{name} the {animal}  "
+
+def test_call_nocode_app(session, runner):
+    writer.ai.apps.generate_content = fake_generate_content
+    session.add_fake_component({
+        "appId": "123",
+        "appInputs": json.dumps({
+            "name": "Koko",
+            "animal": "Hamster"    
+        })
+    })
+    block = WriterNoCodeApp("fake_id", runner, {})
+    block.run()
+    assert block.result == "Koko the Hamster"
+    assert block.outcome == "success"
+
+
+def test_call_nocode_app_missing_appid(session, runner):
+    writer.ai.apps.generate_content = fake_generate_content
+    session.add_fake_component({
+        "appId": "",
+        "appInputs": json.dumps({
+            "name": "Momo",
+            "animal": "Squirrel"    
+        })
+    })
+    block = WriterNoCodeApp("fake_id", runner, {})
+    
+    with pytest.raises(ValueError):
+        block.run()
\ No newline at end of file
diff --git a/tests/backend/test_core.py b/tests/backend/test_core.py
index dbada5043..b22567462 100644
--- a/tests/backend/test_core.py
+++ b/tests/backend/test_core.py
@@ -17,7 +17,6 @@
 from writer import audit_and_fix, wf_project
 from writer.core import (
     BytesWrapper,
-    Evaluator,
     EventDeserialiser,
     FileWrapper,
     MutableValue,
@@ -29,14 +28,10 @@
     import_failure,
     parse_state_variable_expression,
 )
-from writer.core_ui import Component
 from writer.ss_types import WriterEvent
 
 from tests.backend import test_app_dir
 from tests.backend.fixtures import (
-    core_ui_fixtures,
-    file_fixtures,
-    load_fixture_content,
     writer_fixtures,
 )
 
@@ -686,9 +681,8 @@ def test_unpickable_members(self) -> None:
 class TestEventDeserialiser:
 
     root_instance_path = [{"componentId": "root", "instanceNumber": 0}]
-    session_state = WriterState(raw_state_dict)
-    component_tree = session.session_component_tree
-    ed = EventDeserialiser(session_state, component_tree)
+    session.session_state = WriterState(raw_state_dict)
+    ed = EventDeserialiser(session)
 
     def test_unknown_no_payload(self) -> None:
         ev = WriterEvent(
@@ -1144,127 +1138,6 @@ def test_polars_df(self) -> None:
         assert table.column("name")[0].as_py() == "Byte"
         assert table.column("length_cm")[2].as_py() == 32
 
-class TestEvaluator:
-
-    def test_evaluate_field_simple(self) -> None:
-
-        instance_path = [
-            {"componentId": "root", "instanceNumber": 0},
-            {"componentId": "4b6f14b0-b2d9-43e7-8aba-8d3e939c1f83", "instanceNumber": 0},
-            {"componentId": "0cd59329-29c8-4887-beee-39794065221e", "instanceNumber": 0}
-
-        ]
-        st = WriterState({
-            "counter": 8
-        })
-        ct = session.session_component_tree
-        e = Evaluator(st, ct)
-        evaluated = e.evaluate_field(instance_path, "text")
-        assert evaluated == "The counter is 8"
-
-    def test_evaluate_field_repeater(self) -> None:
-        instance_path_base = [
-            {"componentId": "root", "instanceNumber": 0},
-            {"componentId": "4b6f14b0-b2d9-43e7-8aba-8d3e939c1f83", "instanceNumber": 0},
-            {"componentId": "f811ca14-8915-443d-8dd3-77ae69fb80f4", "instanceNumber": 0}
-        ]
-        instance_path_0 = instance_path_base + [
-            {"componentId": "2e688107-f865-419b-a07b-95103197e3fd", "instanceNumber": 0}
-        ]
-        instance_path_2 = instance_path_base + [
-            {"componentId": "2e688107-f865-419b-a07b-95103197e3fd", "instanceNumber": 2}
-        ]
-        st = WriterState({
-            "prog_languages": {
-                "c": "C",
-                "py": "Python",
-                "js": "JavaScript",
-                "ts": "TypeScript"
-            }
-        })
-        ct = session.session_component_tree
-        e = Evaluator(st, ct)
-        assert e.evaluate_field(
-            instance_path_0, "text") == "The id is c and the name is C"
-        assert e.evaluate_field(
-            instance_path_2, "text") == "The id is js and the name is JavaScript"
-
-    def test_set_state(self) -> None:
-        instance_path = [
-            {"componentId": "root", "instanceNumber": 0}
-        ]
-        st = WriterState(raw_state_dict)
-        ct = session.session_component_tree
-        e = Evaluator(st, ct)
-        e.set_state("name", instance_path, "Roger")
-        e.set_state("dynamic_prop", instance_path, "height")
-        e.set_state("features[dynamic_prop]", instance_path, "toddler height")
-        e.set_state("features.new_feature", instance_path, "blue")
-        assert st["name"] == "Roger"
-        assert st["features"]["height"] == "toddler height"
-        assert st["features"]["new_feature"] == "blue"
-
-    def test_evaluate_expression(self) -> None:
-        instance_path = [
-            {"componentId": "root", "instanceNumber": 0}
-        ]
-        st = WriterState(raw_state_dict)
-        ct = session.session_component_tree
-        e = Evaluator(st, ct)
-        assert e.evaluate_expression("features.eyes", instance_path) == "green"
-        assert e.evaluate_expression("best_feature", instance_path) == "eyes"
-        assert e.evaluate_expression("features[best_feature]", instance_path) == "green"
-        assert e.evaluate_expression("a\.b", instance_path) == 3
-
-    def test_get_context_data_should_return_the_target_of_event(self) -> None:
-        """
-        Test that the target of the event is correctly returned by the get_context_data method
-
-        Here we reproduce a click on a button
-        """
-        # Given
-        st = WriterState({})
-        ct = core_ui_fixtures.build_fake_component_tree([
-            Component(id="button1", parentId="root", type="button")
-        ], init_root=True)
-
-        e = Evaluator(st, ct)
-
-        # When
-        context = e.get_context_data([
-            {"componentId": "root", "instanceNumber": 0},
-            {"componentId": "button1", "instanceNumber": 0}
-        ])
-
-        # Then
-        assert context.get("target") == "button1"
-
-    def test_get_context_data_should_return_the_repeater_position_and_the_target_inside_the_repeater(self) -> None:
-        """
-        Test that the repeater position and target of the event is correctly returned by the get_context_data method
-
-        Here we reproduce a click on a button
-        """
-        # Given
-        st = WriterState({})
-        ct = core_ui_fixtures.build_fake_component_tree([
-            Component(id="repeater1", parentId="root", type="repeater", content={'keyVariable': 'item', 'valueVariable': 'value', 'repeaterObject': json.dumps({'a': 'A', 'b': 'B'})}),
-            Component(id="button1", parentId="repeater1", type="button")
-        ], init_root=True)
-
-        e = Evaluator(st, ct)
-
-        # When
-        context = e.get_context_data([
-            {"componentId": "root", "instanceNumber": 0},
-            {"componentId": "repeater1", "instanceNumber": 0},
-            {"componentId": "button1", "instanceNumber": 1}
-        ])
-
-        # Then
-        assert context.get("target") == "button1"
-        assert context.get("item") == "b"
-        assert context.get("value") == "B"
 
 class TestSessionManager:
 
diff --git a/tests/backend/test_evaluator.py b/tests/backend/test_evaluator.py
new file mode 100644
index 000000000..b4cb1ed39
--- /dev/null
+++ b/tests/backend/test_evaluator.py
@@ -0,0 +1,166 @@
+import json
+
+import numpy as np
+import writer as wf
+from writer import audit_and_fix, evaluator, wf_project
+from writer.core import (
+    WriterState,
+)
+from writer.core_ui import Component
+
+from tests.backend import test_app_dir
+from tests.backend.fixtures import (
+    core_ui_fixtures,
+)
+
+raw_state_dict = {
+    "name": "Robert",
+    "age": 1,
+    "interests": ["lamps", "cars"],
+    "state.with.dots": {
+        "photo.jpeg": "Not available",
+    },
+    "features": {
+        "eyes": "green",
+        "height": "very short"
+    },
+    "best_feature": "eyes",
+    "utfࠀ": 23,
+    "counter": 4,
+    "_private": 3,
+    # Used as an example of something unserialisable yet pickable
+    "_private_unserialisable": np.array([[1+2j, 2, 3+3j]]),
+    "a.b": 3
+}
+
+simple_dict = {"items": {
+        "Apple": {"name": "Apple", "type": "fruit"},
+        "Cucumber": {"name": "Cucumber", "type": "vegetable"},
+        "Lettuce": {"name": "Lettuce", "type": "vegetable"}
+    }}
+
+wf.Config.is_mail_enabled_for_log = True
+wf.init_state(raw_state_dict)
+
+_, sc = wf_project.read_files(test_app_dir)
+sc = audit_and_fix.fix_components(sc)
+
+session = wf.session_manager.get_new_session()
+session.session_component_tree.ingest(sc)
+
+class TestEvaluator:
+
+    def test_evaluate_field_simple(self) -> None:
+
+        instance_path = [
+            {"componentId": "root", "instanceNumber": 0},
+            {"componentId": "4b6f14b0-b2d9-43e7-8aba-8d3e939c1f83", "instanceNumber": 0},
+            {"componentId": "0cd59329-29c8-4887-beee-39794065221e", "instanceNumber": 0}
+
+        ]
+        session.session_state = WriterState({
+            "counter": 8
+        })
+        e = evaluator.Evaluator(session.session_state, session.session_component_tree)
+        evaluated = e.evaluate_field(instance_path, "text")
+        assert evaluated == "The counter is 8"
+
+    def test_evaluate_field_repeater(self) -> None:
+        instance_path_base = [
+            {"componentId": "root", "instanceNumber": 0},
+            {"componentId": "4b6f14b0-b2d9-43e7-8aba-8d3e939c1f83", "instanceNumber": 0},
+            {"componentId": "f811ca14-8915-443d-8dd3-77ae69fb80f4", "instanceNumber": 0}
+        ]
+        instance_path_0 = instance_path_base + [
+            {"componentId": "2e688107-f865-419b-a07b-95103197e3fd", "instanceNumber": 0}
+        ]
+        instance_path_2 = instance_path_base + [
+            {"componentId": "2e688107-f865-419b-a07b-95103197e3fd", "instanceNumber": 2}
+        ]
+        session.session_state = WriterState({
+            "prog_languages": {
+                "c": "C",
+                "py": "Python",
+                "js": "JavaScript",
+                "ts": "TypeScript"
+            }
+        })
+        e = evaluator.Evaluator(session.session_state, session.session_component_tree)
+        assert e.evaluate_field(
+            instance_path_0, "text") == "The id is c and the name is C"
+        assert e.evaluate_field(
+            instance_path_2, "text") == "The id is js and the name is JavaScript"
+
+    def test_set_state(self) -> None:
+        instance_path = [
+            {"componentId": "root", "instanceNumber": 0}
+        ]
+        session.session_state = WriterState(raw_state_dict)
+        e = evaluator.Evaluator(session.session_state, session.session_component_tree)
+        e.set_state("name", instance_path, "Roger")
+        e.set_state("dynamic_prop", instance_path, "height")
+        e.set_state("features[dynamic_prop]", instance_path, "toddler height")
+        e.set_state("features.new_feature", instance_path, "blue")
+        assert session.session_state["name"] == "Roger"
+        assert session.session_state["features"]["height"] == "toddler height"
+        assert session.session_state["features"]["new_feature"] == "blue"
+
+    def test_evaluate_expression(self) -> None:
+        instance_path = [
+            {"componentId": "root", "instanceNumber": 0}
+        ]
+        session.session_state = WriterState(raw_state_dict)
+        e = evaluator.Evaluator(session.session_state, session.session_component_tree)
+        assert e.evaluate_expression("features.eyes", instance_path) == "green"
+        assert e.evaluate_expression("best_feature", instance_path) == "eyes"
+        assert e.evaluate_expression("features[best_feature]", instance_path) == "green"
+        assert e.evaluate_expression("a\.b", instance_path) == 3
+
+    def test_get_context_data_should_return_the_target_of_event(self) -> None:
+        """
+        Test that the target of the event is correctly returned by the get_context_data method
+
+        Here we reproduce a click on a button
+        """
+        # Given
+
+        session.session_component_tree = core_ui_fixtures.build_fake_component_tree([
+            Component(id="button1", parentId="root", type="button")
+        ], init_root=True)
+
+        e = evaluator.Evaluator(session.session_state, session.session_component_tree)
+
+        # When
+        context = e.get_context_data([
+            {"componentId": "root", "instanceNumber": 0},
+            {"componentId": "button1", "instanceNumber": 0}
+        ])
+
+        # Then
+        assert context.get("target") == "button1"
+
+    def test_get_context_data_should_return_the_repeater_position_and_the_target_inside_the_repeater(self) -> None:
+        """
+        Test that the repeater position and target of the event is correctly returned by the get_context_data method
+
+        Here we reproduce a click on a button
+        """
+        # Given
+        session.session_component_tree = core_ui_fixtures.build_fake_component_tree([
+            Component(id="repeater1", parentId="root", type="repeater", content={'keyVariable': 'item', 'valueVariable': 'value', 'repeaterObject': json.dumps({'a': 'A', 'b': 'B'})}),
+            Component(id="button1", parentId="repeater1", type="button")
+        ], init_root=True)
+
+        e = evaluator.Evaluator(session.session_state, session.session_component_tree)
+
+        # When
+        context = e.get_context_data([
+            {"componentId": "root", "instanceNumber": 0},
+            {"componentId": "repeater1", "instanceNumber": 0},
+            {"componentId": "button1", "instanceNumber": 1}
+        ])
+
+        # Then
+        assert context.get("target") == "button1"
+        assert context.get("item") == "b"
+        assert context.get("value") == "B"
\ No newline at end of file
diff --git a/tests/e2e/presets/workflows/.wf/components-page-0-c0f99a9e-5004-4e75-a6c6-36f17490b134.jsonl b/tests/e2e/presets/workflows/.wf/components-page-0-c0f99a9e-5004-4e75-a6c6-36f17490b134.jsonl
index 110c00bf7..ee3033be5 100644
--- a/tests/e2e/presets/workflows/.wf/components-page-0-c0f99a9e-5004-4e75-a6c6-36f17490b134.jsonl
+++ b/tests/e2e/presets/workflows/.wf/components-page-0-c0f99a9e-5004-4e75-a6c6-36f17490b134.jsonl
@@ -2,4 +2,4 @@
 {"id": "bebc5fe9-63a7-46a7-b0fa-62303555cfaf", "type": "header", "content": {"text": "Workflows Test App"}, "handlers": {}, "isCodeManaged": false, "parentId": "c0f99a9e-5004-4e75-a6c6-36f17490b134", "position": 0, "visible": {"binding": "", "expression": true, "reversed": false}}
 {"id": "ixxb26ukbvr0sknw", "type": "repeater", "content": {"keyVariable": "itemId", "repeaterObject": "{ \"pl\": { \"object\": \"plant\" }, \"cu\": { \"object\": \"cup\" }}", "valueVariable": "item"}, "handlers": {}, "isCodeManaged": false, "parentId": "c0f99a9e-5004-4e75-a6c6-36f17490b134", "position": 1}
 {"id": "iftqnmjw8ipaknex", "type": "section", "content": {"title": "@{itemId}: @{item.object}"}, "handlers": {}, "isCodeManaged": false, "parentId": "ixxb26ukbvr0sknw", "position": 0}
-{"id": "7no34ag7gmwgm1rd", "type": "textinput", "content": {"label": ""}, "handlers": {"wf-change": "$runWorkflow_handle_object"}, "isCodeManaged": false, "parentId": "iftqnmjw8ipaknex", "position": 0}
+{"id": "7no34ag7gmwgm1rd", "type": "textinput", "content": {"label": "", "placeholder": "@{item.object}"}, "handlers": {"wf-change": "$runWorkflow_handle_object"}, "isCodeManaged": false, "parentId": "iftqnmjw8ipaknex", "position": 0}
diff --git a/tests/e2e/presets/workflows/.wf/components-page-1-i9io5f734z9esrxs.jsonl b/tests/e2e/presets/workflows/.wf/components-page-1-i9io5f734z9esrxs.jsonl
deleted file mode 100644
index 5a00a5f42..000000000
--- a/tests/e2e/presets/workflows/.wf/components-page-1-i9io5f734z9esrxs.jsonl
+++ /dev/null
@@ -1,2 +0,0 @@
-{"id": "i9io5f734z9esrxs", "type": "page", "content": {}, "handlers": {}, "isCodeManaged": false, "parentId": "root", "position": 1}
-{"id": "16eeo21o6k8tcxf7", "type": "chatbot", "content": {"conversation": "@{convo}"}, "handlers": {"wf-chatbot-message": "$runWorkflow_handle_object"}, "isCodeManaged": false, "parentId": "i9io5f734z9esrxs", "position": 0}
diff --git a/tests/e2e/presets/workflows/.wf/components-workflows_workflow-0-auxjfi7lssb268ly.jsonl b/tests/e2e/presets/workflows/.wf/components-workflows_workflow-0-auxjfi7lssb268ly.jsonl
index c9267239c..4216ffb42 100644
--- a/tests/e2e/presets/workflows/.wf/components-workflows_workflow-0-auxjfi7lssb268ly.jsonl
+++ b/tests/e2e/presets/workflows/.wf/components-workflows_workflow-0-auxjfi7lssb268ly.jsonl
@@ -1,6 +1,4 @@
 {"id": "auxjfi7lssb268ly", "type": "workflows_workflow", "content": {"key": "handle_object"}, "handlers": {}, "isCodeManaged": false, "parentId": "workflows_root", "position": 0}
-{"id": "bgfri5xbo3l5916z", "type": "workflows_writeraddchatmessage", "content": {"conversationStateElement": "convo", "message": "@{payload}"}, "handlers": {}, "isCodeManaged": false, "outs": [{"toNodeId": "36w4ghu0oioub912", "outId": "success"}], "parentId": "auxjfi7lssb268ly", "position": 0, "x": 473, "y": 204}
-{"id": "36w4ghu0oioub912", "type": "workflows_writerchat", "content": {"conversationStateElement": "convo", "tools": "{\"get_employee_info\":{\"description\":\"Gets info for an employee, given an employee id\",\"parameters\":{\"id\":{\"type\":\"string\",\"description\":\"Id of the employee\"}},\"type\":\"function\"}}", "useStreaming": "no"}, "handlers": {}, "isCodeManaged": false, "outs": [{"toNodeId": "6ktplk37vue14rog", "outId": "tools_get_employee_info"}], "parentId": "auxjfi7lssb268ly", "position": 1, "x": 889, "y": 173}
-{"id": "6ktplk37vue14rog", "type": "workflows_httprequest", "content": {"url": "https://reqres.in/api/users/@{id}"}, "handlers": {}, "isCodeManaged": false, "outs": [{"toNodeId": "8ly2cojv5m77lfpd", "outId": "success"}], "parentId": "auxjfi7lssb268ly", "position": 2, "x": 1382, "y": 152}
-{"id": "i183fmlmluglk2tg", "type": "workflows_writerinitchat", "content": {"alias": "", "conversationStateElement": "convo"}, "handlers": {}, "isCodeManaged": false, "outs": [{"toNodeId": "bgfri5xbo3l5916z", "outId": "success"}], "parentId": "auxjfi7lssb268ly", "position": 3, "x": 52, "y": 203}
-{"id": "8ly2cojv5m77lfpd", "type": "workflows_returnvalue", "content": {"value": "@{result.body}"}, "handlers": {}, "isCodeManaged": false, "parentId": "auxjfi7lssb268ly", "position": 4, "x": 1744, "y": 170}
+{"id": "8y56lmia3wu99jhl", "type": "workflows_parsejson", "content": {"plainText": "{\"color\": \"@{payload}\", \"object\": \"@{context.item.object}\"}"}, "handlers": {}, "isCodeManaged": false, "outs": [{"toNodeId": "xy6vdzh2pm55alc0", "outId": "success"}], "parentId": "auxjfi7lssb268ly", "position": 0, "x": 150, "y": 319}
+{"id": "xy6vdzh2pm55alc0", "type": "workflows_setstate", "content": {"alias": "Save the JSON", "element": "json_e2e", "value": "@{result}"}, "handlers": {}, "isCodeManaged": false, "outs": [{"toNodeId": "mve8ssvtk0pvw5yf", "outId": "success"}], "parentId": "auxjfi7lssb268ly", "position": 1, "x": 537, "y": 321}
+{"id": "mve8ssvtk0pvw5yf", "type": "workflows_returnvalue", "content": {"alias": "", "value": "@{json_e2e}"}, "handlers": {}, "isCodeManaged": false, "parentId": "auxjfi7lssb268ly", "position": 2, "x": 876, "y": 317}
diff --git a/tests/e2e/presets/workflows/.wf/metadata.json b/tests/e2e/presets/workflows/.wf/metadata.json
index cab48d17b..da9c77c7c 100644
--- a/tests/e2e/presets/workflows/.wf/metadata.json
+++ b/tests/e2e/presets/workflows/.wf/metadata.json
@@ -1,3 +1,3 @@
 {
-    "writer_version": "0.8.0rc6"
+    "writer_version": "0.8.0rc3"
 }
\ No newline at end of file
diff --git a/tests/e2e/tests/reuse.spec.ts b/tests/e2e/tests/reuse.spec.ts
index a2c27a134..c24a49fed 100644
--- a/tests/e2e/tests/reuse.spec.ts
+++ b/tests/e2e/tests/reuse.spec.ts
@@ -45,7 +45,7 @@ test.describe("Reuse component", () => {
 	};
 
 	const closeSettingsBar = async (page: Page) => {
-		await page.locator('.BuilderSettings button[data-automation-action="close"]').click();
+		await page.locator('[data-automation-action="close-settings"]').click();
 	}
 
 	const removeComponent = async (page: Page, selector: string) => {
diff --git a/tests/e2e/tests/undoRedo.spec.ts b/tests/e2e/tests/undoRedo.spec.ts
index cd758adc6..99e023372 100644
--- a/tests/e2e/tests/undoRedo.spec.ts
+++ b/tests/e2e/tests/undoRedo.spec.ts
@@ -8,7 +8,7 @@ test.describe('undo and redo', () => {
 	let url: string;
 
 	const closeSettingsBar = async (page: Page) => {
-		await page.locator('.BuilderSettings button[data-automation-action="close"]').click();
+		await page.locator('.BuilderSettings button[data-automation-action="close-settings"]').click();
 	}
 
 	test.beforeAll(async ({ request }) => {
diff --git a/tests/e2e/tests/workflows.spec.ts b/tests/e2e/tests/workflows.spec.ts
index 7d4bd980a..41237c906 100644
--- a/tests/e2e/tests/workflows.spec.ts
+++ b/tests/e2e/tests/workflows.spec.ts
@@ -1,23 +1,15 @@
-/*
 import { test, expect } from "@playwright/test";
 
-const setTextField = async (page, text) => {
-	await page.locator('div.CoreText.component').click();
-	await page
-		.locator('.BuilderFieldsText[data-automation-key="text"] .templateInput')
-		.fill(text);
-}
-
-test.describe("state autocompletion", () => {
+test.describe("Workflows", () => {
 	let url: string;
 
-	test.beforeAll(async ({request}) => {
+	test.beforeAll(async ({ request }) => {
 		const response = await request.post(`/preset/workflows`);
 		expect(response.ok()).toBeTruthy();
-		({url} = await response.json());
+		({ url } = await response.json());
 	});
 
-	test.afterAll(async ({request}) => {
+	test.afterAll(async ({ request }) => {
 		await request.delete(url);
 	});
 
@@ -25,19 +17,92 @@ test.describe("state autocompletion", () => {
 		await page.goto(url);
 	});
 
-	test.describe("text", () => {
-		test("completion", async ({ page }) => {
-			
-			const instancePaths = ["root:0,c0f99a9e-5004-4e75-a6c6-36f17490b134:0,ixxb26ukbvr0sknw:0,iftqnmjw8ipaknex:0,7no34ag7gmwgm1rd:0", "root:0,c0f99a9e-5004-4e75-a6c6-36f17490b134:0,ixxb26ukbvr0sknw:0,iftqnmjw8ipaknex:0,7no34ag7gmwgm1rd:0"];
-			
-			await setTextField(page, "@{types.");
-			page.locator('.BuilderFieldsText[data-automation-key="text"] .fieldStateAutocomplete span.prop:text-matches("string")').click();
-			await expect(page
-				.locator('.BuilderFieldsText[data-automation-key="text"] .templateInput'))
-				.toHaveValue("@{types.string");
-		});
+	const inputData = [
+		{ object: "plant", color: "green" },
+		{ object: "cup", color: "pink" },
+	];
 
+	inputData.forEach(({ object, color }) => {
+		test(`Test context and payload in Workflows for ${object} ${color}`, async ({
+			page,
+		}) => {
+			await page.getByPlaceholder(object).fill(color);
+			await page.locator(`[data-automation-action="toggle-log-panel"]`).click();
+			const rowLocator = page
+				.locator(".BuilderLogPanel div.row")
+				.filter({ hasText: "Return value" });
+			await rowLocator.getByRole("button", { name: "Details" }).click();
+			const resultsLocator = page.locator(
+				`.BuilderModal [data-automation-key="result"]`,
+			);
+			const returnValueLocator = page.locator(
+				`.BuilderModal [data-automation-key="return-value"]`,
+			);
+			const expectedTexts = ["color", color, "object", object];
+			expectedTexts.forEach(
+				async (text) => await expect(resultsLocator).toContainText(text),
+			);
+			expectedTexts.forEach(
+				async (text) => await expect(returnValueLocator).toContainText(text),
+			);
+		});
 	});
 
-});
-*/
\ No newline at end of file
+	test("Create workflow and run workflow handle_object from it", async ({
+		page,
+	}) => {
+		await page.locator(`[data-automation-action="set-mode-workflows"]`).click();
+		await page.locator(`[data-automation-action="add-workflow"]`).click();
+
+		await page
+			.locator(
+				`div.component.button[data-component-type="workflows_runworkflow"]`,
+			)
+			.dragTo(page.locator(".WorkflowsWorkflow"), {
+				targetPosition: { x: 100, y: 100 },
+			});
+		const runWorkflowBlock = page.locator(`.WorkflowsNode.wf-type-workflows_runworkflow`);
+
+		await page
+			.locator(
+				`div.component.button[data-component-type="workflows_returnvalue"]`,
+			)
+			.dragTo(page.locator(".WorkflowsWorkflow"), {
+				targetPosition: { x: 400, y: 100 },
+			});
+		const returnValueBlock = page.locator(`.WorkflowsNode.wf-type-workflows_returnvalue`);
+
+		await runWorkflowBlock.click();
+		await page.locator(`.BuilderFieldsText[data-automation-key="workflowKey"] input`).fill("handle_object");
+		const executionEnv = {
+			"payload": "blue",
+			"context": {
+				"item": {
+					"object": "bottle"
+				}
+			}
+		};
+		await page.locator(`.BuilderFieldsObject[data-automation-key="executionEnv"] textarea`).fill(JSON.stringify(executionEnv));
+		await page.locator(`[data-automation-action="close-settings"]`).click();
+
+		await runWorkflowBlock.locator(".ball.success").dragTo(returnValueBlock);
+
+		await returnValueBlock.click();
+		await page.locator(`.BuilderFieldsText[data-automation-key="value"] textarea`).fill("@{result}");
+
+		await page.locator(`[data-automation-action="run-workflow"]`).click();
+
+		await page.locator(`[data-automation-action="toggle-log-panel"]`).click();
+		const rowLocator = page
+			.locator(".BuilderLogPanel div.row")
+			.filter({ hasText: "Return value" }).first();;
+		await rowLocator.getByRole("button", { name: "Details" }).click();
+		const returnValueLocator = page.locator(
+			`.BuilderModal [data-automation-key="return-value"]`,
+		);
+		const expectedTexts = ["color", "blue", "object", "bottle"];
+		expectedTexts.forEach(
+			async (text) => await expect(returnValueLocator).toContainText(text),
+		);
+	});
+});
\ No newline at end of file