diff --git a/.github/workflows/nix-flake-check.yml b/.github/workflows/nix-flake-check.yml
new file mode 100644
index 0000000..8a22233
--- /dev/null
+++ b/.github/workflows/nix-flake-check.yml
@@ -0,0 +1,14 @@
+name: Flake check
+
+on:
+  pull_request:
+  push:
+  workflow_call:
+
+jobs:
+  nix-flake-check:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - uses: DeterminateSystems/nix-installer-action@v10
+    - run: nix flake check -L
diff --git a/.gitignore b/.gitignore
index df1bddf..8d3ec8e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,6 +6,7 @@
 
 # Meta
 !LICENSE
+!TODO.md
 
 # Nix
 !nix/
diff --git a/TODO.md b/TODO.md
new file mode 100644
index 0000000..9a743e6
--- /dev/null
+++ b/TODO.md
@@ -0,0 +1,7 @@
+# TODO
+
+- [x] Add testing and linting to CI
+- [ ] Add iter spec
+- [ ] Add basic technical spec
+- [ ] Create the module system based on the spec (+ tests)
+- [ ] Create the first module (preamble) (+ tests)