diff --git a/generativeai/src/main/java/com/google/ai/client/generativeai/internal/api/client/Types.kt b/generativeai/src/main/java/com/google/ai/client/generativeai/internal/api/client/Types.kt
index 8f647bf1..abd0e545 100644
--- a/generativeai/src/main/java/com/google/ai/client/generativeai/internal/api/client/Types.kt
+++ b/generativeai/src/main/java/com/google/ai/client/generativeai/internal/api/client/Types.kt
@@ -26,7 +26,7 @@ internal data class GenerationConfig(
   @SerialName("top_k") val topK: Int?,
   @SerialName("candidate_count") val candidateCount: Int?,
   @SerialName("max_output_tokens") val maxOutputTokens: Int?,
-  @SerialName("stop_sequences") val stopSequences: List<String>?
+  @SerialName("stop_sequences") val stopSequences: List<String>?,
 )
 
 @Serializable internal data class Tool(val functionDeclarations: List<FunctionDeclaration>)
@@ -35,20 +35,16 @@ internal data class GenerationConfig(
 internal data class FunctionDeclaration(
   val name: String,
   val description: String,
-  val parameters: FunctionParameters
-)
-
-@Serializable
-internal data class FunctionParameters(
-  val properties: Map<String, FunctionParameterProperties>,
-  val required: List<String>,
-  val type: String,
+  val parameters: FunctionParameterProperties,
 )
 
 @Serializable
 internal data class FunctionParameterProperties(
   val type: String,
-  val description: String,
-  val format: String?,
-  val enum: List<String>?
+  val description: String? = null,
+  val format: String? = null,
+  val enum: List<String>? = null,
+  val properties: Map<String, FunctionParameterProperties>? = null,
+  val required: List<String>? = null,
+  val items: FunctionParameterProperties? = null
 )
diff --git a/generativeai/src/main/java/com/google/ai/client/generativeai/internal/util/conversions.kt b/generativeai/src/main/java/com/google/ai/client/generativeai/internal/util/conversions.kt
index cfd5c533..33e5e5f4 100644
--- a/generativeai/src/main/java/com/google/ai/client/generativeai/internal/util/conversions.kt
+++ b/generativeai/src/main/java/com/google/ai/client/generativeai/internal/util/conversions.kt
@@ -123,15 +123,23 @@ internal fun FunctionDeclaration.toInternal() =
   com.google.ai.client.generativeai.internal.api.client.FunctionDeclaration(
     name,
     description,
-    com.google.ai.client.generativeai.internal.api.client.FunctionParameters(
-      getParameters().associate { it.name to it.toInternal() },
-      getParameters().map { it.name },
-      "OBJECT",
+    FunctionParameterProperties(
+      properties = getParameters().associate { it.name to it.toInternal() },
+      required = getParameters().map { it.name },
+      type = "OBJECT",
     ),
   )
 
-internal fun <T> ParameterDeclaration<T>.toInternal() =
-  FunctionParameterProperties(type.name, description, format, enum)
+internal fun <T> ParameterDeclaration<T>.toInternal(): FunctionParameterProperties =
+  FunctionParameterProperties(
+    type.name,
+    description,
+    format,
+    enum,
+    properties?.mapValues { it.value.toInternal() },
+    required,
+    items?.toInternal()
+  )
 
 internal fun JSONObject.toInternal() = Json.decodeFromString<JsonObject>(toString())
 
diff --git a/generativeai/src/main/java/com/google/ai/client/generativeai/type/FunctionDeclarations.kt b/generativeai/src/main/java/com/google/ai/client/generativeai/type/FunctionDeclarations.kt
index 1aafb2cc..642596d2 100644
--- a/generativeai/src/main/java/com/google/ai/client/generativeai/type/FunctionDeclarations.kt
+++ b/generativeai/src/main/java/com/google/ai/client/generativeai/type/FunctionDeclarations.kt
@@ -169,12 +169,20 @@ abstract class FunctionDeclaration(val name: String, val description: String) {
  *   int/float or keywords like "enum" for the string type
  * @property enum: contains the enum values for a string enum
  * @property type: contains the type info and parser
+ * @property properties: if type is OBJECT, then this contains the description of the fields of the
+ *   object by name
+ * @property required: if type is OBJECT, then this contains the list of required keys
+ * @property items: if the type is ARRAY, then this contains a description of the objects in the
+ *   array
  */
 class ParameterDeclaration<T>(
   val name: String,
   val description: String,
   val format: String? = null,
   val enum: List<String>? = null,
+  val properties: Map<String, ParameterDeclaration<Any>>? = null,
+  val required: List<String>? = null,
+  val items: ParameterDeclaration<Any>? = null,
   val type: FunctionType<T>,
 ) {
   fun fromString(value: String?) = type.parse(value)