diff --git a/pdl-live-react/src/pdl_ast.d.ts b/pdl-live-react/src/pdl_ast.d.ts
index 7a47607b7..7da0f4cc7 100644
--- a/pdl-live-react/src/pdl_ast.d.ts
+++ b/pdl-live-react/src/pdl_ast.d.ts
@@ -40,20 +40,6 @@ export type Program =
  *
  */
 export type Description = string | null
-export type PdlTypeType =
-  | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
-  | EnumPdlType
-  | StrPdlType
-  | FloatPdlType
-  | IntPdlType
-  | ListPdlType
-  | PdlTypeType[]
-  | OptionalPdlType
-  | JsonSchemaTypePdlType
-  | ObjPdlType
-  | {
-      [k: string]: PdlTypeType
-    }
 export type Enum = unknown[]
 export type Minlength = number | null
 export type Maxlength = number | null
@@ -68,12 +54,27 @@ export type Exclusiveminimum1 = number | null
 export type Maximum1 = number | null
 export type Exclusivemaximum1 = number | null
 export type List = PdlTypeType | ListPdlTypeConstraints
-export type Minitems = number | null
-export type Maxitems = number | null
+export type PdlTypeType =
+  | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+  | EnumPdlType
+  | StrPdlType
+  | FloatPdlType
+  | IntPdlType
+  | ListPdlType
+  | PdlTypeType[]
+  | OptionalPdlType
+  | JsonSchemaTypePdlType
+  | ObjPdlType
+  | {
+      [k: string]: PdlTypeType
+    }
+  | null
 export type Type = string | string[]
 export type Obj = {
   [k: string]: PdlTypeType
 } | null
+export type Minitems = number | null
+export type Maxitems = number | null
 /**
  * Documentation associated to the block.
  *
@@ -2838,7 +2839,7 @@ export type Function = {
   [k: string]: PdlTypeType
 } | null
 /**
- * Body of the function
+ * Body of the function.
  *
  */
 export type Return =
@@ -2867,6 +2868,11 @@ export type Return =
   | ErrorBlock
   | EmptyBlock
   | null
+/**
+ * Function signature computed from the function definition.
+ *
+ */
+export type Signature = string | null
 export type PdlBlock =
   | boolean
   | number
@@ -2903,7 +2909,21 @@ export interface FunctionBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs
   def?: Def24
   contribute?: Contribute20
@@ -2921,6 +2941,7 @@ export interface FunctionBlock {
   kind?: Kind20
   function: Function
   return: Return
+  signature?: Signature
 }
 /**
  * Enumerated type.
@@ -2979,14 +3000,6 @@ export interface IntPdlTypeConstraints {
 export interface ListPdlType {
   list: List
 }
-/**
- * Constraints on list type.
- */
-export interface ListPdlTypeConstraints {
-  minItems?: Minitems
-  maxItems?: Maxitems
-  [k: string]: unknown
-}
 /**
  * Optional type.
  */
@@ -3001,11 +3014,19 @@ export interface JsonSchemaTypePdlType {
   [k: string]: unknown
 }
 /**
- * Optional type.
+ * Object type.
  */
 export interface ObjPdlType {
   obj: Obj
 }
+/**
+ * Constraints on list type.
+ */
+export interface ListPdlTypeConstraints {
+  minItems?: Minitems
+  maxItems?: Maxitems
+  [k: string]: unknown
+}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -3047,7 +3068,21 @@ export interface CallBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs1
   def?: Def23
   contribute?: Contribute19
@@ -3115,7 +3150,21 @@ export interface LitellmModelBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs2
   def?: Def22
   contribute?: Contribute18
@@ -3184,7 +3233,21 @@ export interface GraniteioModelBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs3
   def?: Def21
   contribute?: Contribute17
@@ -3264,7 +3327,21 @@ export interface CodeBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs4
   def?: Def20
   contribute?: Contribute16
@@ -3332,7 +3409,21 @@ export interface ArgsBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs5
   def?: Def19
   contribute?: Contribute15
@@ -3394,7 +3485,21 @@ export interface GetBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs6
   def?: Def18
   contribute?: Contribute14
@@ -3474,7 +3579,21 @@ export interface DataBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs7
   def?: Def17
   contribute?: Contribute13
@@ -3544,7 +3663,21 @@ export interface IfBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs8
   def?: Def16
   contribute?: Contribute12
@@ -3624,7 +3757,21 @@ export interface MatchBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs9
   def?: Def11
   contribute?: Contribute11
@@ -3694,7 +3841,21 @@ export interface RepeatBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs10
   def?: Def10
   contribute?: Contribute10
@@ -3760,7 +3921,21 @@ export interface TextBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs11
   def?: Def9
   contribute?: Contribute9
@@ -3820,7 +3995,21 @@ export interface LastOfBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs12
   def?: Def8
   contribute?: Contribute8
@@ -3880,7 +4069,21 @@ export interface ArrayBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs13
   def?: Def7
   contribute?: Contribute7
@@ -3940,7 +4143,21 @@ export interface ObjectBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs14
   def?: Def6
   contribute?: Contribute6
@@ -4000,7 +4217,21 @@ export interface MessageBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs15
   def?: Def5
   contribute?: Contribute5
@@ -4073,7 +4304,21 @@ export interface ReadBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs16
   def?: Def4
   contribute?: Contribute4
@@ -4134,7 +4379,21 @@ export interface IncludeBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs17
   def?: Def3
   contribute?: Contribute3
@@ -4195,7 +4454,21 @@ export interface ImportBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs18
   def?: Def2
   contribute?: Contribute2
@@ -4255,7 +4528,21 @@ export interface ErrorBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs19
   def?: Def1
   contribute?: Contribute1
@@ -4315,7 +4602,21 @@ export interface EmptyBlock {
    * Type specification of the result of the block.
    *
    */
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   defs?: Defs20
   def?: Def
   contribute?: Contribute
@@ -4388,7 +4689,21 @@ export interface Table {
 }
 export interface PdlParser {
   description?: Description21
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   pdl: Pdl
 }
 /**
@@ -4396,7 +4711,21 @@ export interface PdlParser {
  */
 export interface RegexParser {
   description?: Description22
-  spec?: PdlTypeType | null
+  spec?:
+    | ("null" | "bool" | "str" | "float" | "int" | "list" | "obj")
+    | EnumPdlType
+    | StrPdlType
+    | FloatPdlType
+    | IntPdlType
+    | ListPdlType
+    | PdlTypeType[]
+    | OptionalPdlType
+    | JsonSchemaTypePdlType
+    | ObjPdlType
+    | {
+        [k: string]: PdlTypeType
+      }
+    | null
   regex: Regex
   mode?: Mode
 }
diff --git a/src/pdl/pdl-schema.json b/src/pdl/pdl-schema.json
index 300a0a6e2..89ed2cdf8 100644
--- a/src/pdl/pdl-schema.json
+++ b/src/pdl/pdl-schema.json
@@ -45,14 +45,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
@@ -451,14 +444,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
@@ -984,14 +970,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
@@ -1480,14 +1459,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
@@ -1995,14 +1967,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
@@ -2399,14 +2364,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
@@ -2797,14 +2755,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
@@ -3361,14 +3312,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
@@ -3817,8 +3761,23 @@
               "type": "null"
             }
           ],
-          "description": "Body of the function\n    ",
+          "description": "Body of the function.\n    ",
           "title": "Return"
+        },
+        "signature": {
+          "anyOf": [
+            {
+              "contentMediaType": "application/json",
+              "contentSchema": {},
+              "type": "string"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "default": null,
+          "description": "Function signature computed from the function definition.\n    ",
+          "title": "Signature"
         }
       },
       "required": [
@@ -3846,14 +3805,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
@@ -4236,14 +4188,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
@@ -4820,14 +4765,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
@@ -5406,14 +5344,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
@@ -5880,14 +5811,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
@@ -6536,14 +6460,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
@@ -7066,14 +6983,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
@@ -8055,14 +7965,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
@@ -8647,14 +8550,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
@@ -9132,7 +9028,7 @@
     },
     "ObjPdlType": {
       "additionalProperties": false,
-      "description": "Optional type.",
+      "description": "Object type.",
       "properties": {
         "obj": {
           "anyOf": [
@@ -9173,14 +9069,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
@@ -9977,14 +9866,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null
         },
         "pdl": {
@@ -10182,6 +10064,9 @@
             "$ref": "#/$defs/PdlTypeType"
           },
           "type": "object"
+        },
+        {
+          "type": "null"
         }
       ]
     },
@@ -10318,14 +10203,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
@@ -10736,14 +10614,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null
         },
         "regex": {
@@ -10787,14 +10658,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
@@ -11519,14 +11383,7 @@
           "title": "Description"
         },
         "spec": {
-          "anyOf": [
-            {
-              "$ref": "#/$defs/PdlTypeType"
-            },
-            {
-              "type": "null"
-            }
-          ],
+          "$ref": "#/$defs/PdlTypeType",
           "default": null,
           "description": "Type specification of the result of the block.\n    "
         },
diff --git a/src/pdl/pdl_ast.py b/src/pdl/pdl_ast.py
index 9abcb24df..9b76d37a1 100644
--- a/src/pdl/pdl_ast.py
+++ b/src/pdl/pdl_ast.py
@@ -19,6 +19,7 @@
     BeforeValidator,
     ConfigDict,
     Field,
+    Json,
     RootModel,
     TypeAdapter,
 )
@@ -236,7 +237,7 @@ class JsonSchemaTypePdlType(PdlType):
 
 
 class ObjPdlType(PdlType):
-    """Optional type."""
+    """Object type."""
 
     obj: Optional[dict[str, "PdlTypeType"]]
 
@@ -244,7 +245,8 @@ class ObjPdlType(PdlType):
 PdlTypeType = TypeAliasType(
     "PdlTypeType",
     Annotated[
-        "Union[BasePdlType,"  # pyright: ignore
+        "Union[None,"  # pyright: ignore
+        "      BasePdlType,"
         "      EnumPdlType,"
         "      StrPdlType,"
         "      FloatPdlType,"
@@ -269,7 +271,7 @@ class Parser(BaseModel):
     description: Optional[str] = None
     """Documentation associated to the parser.
     """
-    spec: Optional[PdlTypeType] = None
+    spec: PdlTypeType = None
     """Expected type of the parsed value.
     """
 
@@ -348,7 +350,7 @@ class Block(BaseModel):
     description: Optional[str] = None
     """Documentation associated to the block.
     """
-    spec: Optional[PdlTypeType] = None
+    spec: PdlTypeType = None
     """Type specification of the result of the block.
     """
     defs: dict[str, "BlockType"] = {}
@@ -416,8 +418,12 @@ class FunctionBlock(LeafBlock):
     """Functions parameters with their types.
     """
     returns: "BlockType" = Field(..., alias="return")
-    """Body of the function
+    """Body of the function.
+    """
+    signature: Optional[Json] = None
+    """Function signature computed from the function definition.
     """
+
     # Field for internal use
     pdl__scope: SkipJsonSchema[Optional[ScopeType]] = Field(default=None, repr=False)
 
diff --git a/src/pdl/pdl_dumper.py b/src/pdl/pdl_dumper.py
index 912ae06e9..a8162fb0d 100644
--- a/src/pdl/pdl_dumper.py
+++ b/src/pdl/pdl_dumper.py
@@ -317,8 +317,10 @@ def expr_to_dict(expr: ExpressionType, json_compatible: bool):
 
 
 def type_to_dict(t: PdlTypeType):
-    d: str | list | dict
+    d: None | str | list | dict
     match t:
+        case None:
+            d = None
         case "null" | "bool" | "str" | "float" | "int" | "list" | "obj":
             d = t
         case EnumPdlType():
diff --git a/src/pdl/pdl_interpreter.py b/src/pdl/pdl_interpreter.py
index 650229ad3..d15a703f6 100644
--- a/src/pdl/pdl_interpreter.py
+++ b/src/pdl/pdl_interpreter.py
@@ -100,6 +100,7 @@
 from .pdl_parser import PDLParseError, parse_file, parse_str  # noqa: E402
 from .pdl_python_repl import PythonREPL  # noqa: E402
 from .pdl_scheduler import yield_background, yield_result  # noqa: E402
+from .pdl_schema_utils import get_json_schema  # noqa: E402
 from .pdl_schema_validator import type_check_args, type_check_spec  # noqa: E402
 from .pdl_utils import (  # noqa: E402
     GeneratorWrapper,
@@ -894,6 +895,16 @@ def process_block_body(
             if block.def_ is not None:
                 scope = scope | {block.def_: closure}
             closure.pdl__scope = scope
+            signature: dict[str, Any] = {"type": "function"}
+            if block.def_ is not None:
+                signature["name"] = block.def_
+            if block.description is not None:
+                signature["description"] = block.description
+            if block.function is not None:
+                signature["parameters"] = get_json_schema(block.function, False) or {}
+            else:
+                signature["parameters"] = {}
+            closure.signature = signature
             result = PdlConst(closure)
             background = PdlList([])
             trace = closure.model_copy(update={})
@@ -976,6 +987,8 @@ def process_defs(
         state = state.with_iter(idx)
         state = state.with_yield_result(False)
         state = state.with_yield_background(False)
+        if isinstance(block, FunctionBlock) and block.def_ is None:
+            block = block.model_copy(update={"def_": x})
         result, _, _, block_trace = process_block(state, scope, block, newloc)
         scope = scope | PdlDict({x: result})
         defs_trace[x] = block_trace
diff --git a/src/pdl/pdl_llms.py b/src/pdl/pdl_llms.py
index 5c0db1a0c..f9d569654 100644
--- a/src/pdl/pdl_llms.py
+++ b/src/pdl/pdl_llms.py
@@ -183,7 +183,7 @@ def generate_text_stream(
 
 
 def set_structured_decoding_parameters(
-    spec: Optional[PdlTypeType],
+    spec: PdlTypeType,
     parameters: Optional[dict[str, Any]],
 ) -> dict[str, Any]:
     if parameters is None:
diff --git a/src/pdl/pdl_schema_utils.py b/src/pdl/pdl_schema_utils.py
index 78071c5ef..f5adb6f22 100644
--- a/src/pdl/pdl_schema_utils.py
+++ b/src/pdl/pdl_schema_utils.py
@@ -44,7 +44,7 @@ def convert_to_json_type(a_type):
 
 
 def pdltype_to_jsonschema(
-    pdl_type: Optional[PdlTypeType], additional_properties: bool
+    pdl_type: PdlTypeType, additional_properties: bool
 ) -> dict[str, Any]:
     schema: dict[str, Any]
     match pdl_type:
diff --git a/src/pdl/pdl_schema_validator.py b/src/pdl/pdl_schema_validator.py
index 160a1e8c4..c84ca5374 100644
--- a/src/pdl/pdl_schema_validator.py
+++ b/src/pdl/pdl_schema_validator.py
@@ -8,7 +8,9 @@
 
 
 def type_check_args(
-    args: Optional[dict[str, Any]], params: Optional[dict[str, Any]], loc
+    args: Optional[dict[str, Any]],
+    params: Optional[dict[str, PdlTypeType]],
+    loc,
 ) -> list[str]:
     if (args == {} or args is None) and (params is None or params == {}):
         return []
@@ -35,7 +37,7 @@ def type_check_args(
     return type_check(args_copy, schema, loc)
 
 
-def type_check_spec(result: Any, spec: Optional[PdlTypeType], loc) -> list[str]:
+def type_check_spec(result: Any, spec: PdlTypeType, loc) -> list[str]:
     schema = pdltype_to_jsonschema(spec, False)
     if schema is None:
         return ["Error obtaining a valid schema from spec"]
diff --git a/tests/test_function.py b/tests/test_function.py
index 1fb2090b6..d78094421 100644
--- a/tests/test_function.py
+++ b/tests/test_function.py
@@ -20,6 +20,17 @@ def test_function_call():
     assert text == "Hello world!"
 
 
+def test_hello_signature():
+    result = exec_dict(hello_def, output="all")
+    closure = result["scope"]["hello"]
+    assert closure.signature == {
+        "name": hello_def["def"],
+        "description": hello_def["description"],
+        "type": "function",
+        "parameters": {},
+    }
+
+
 hello_params = {
     "description": "Call hello",
     "text": [
@@ -39,6 +50,22 @@ def test_function_params():
     assert text == "Hello World!"
 
 
+def test_hello_params_signature():
+    result = exec_dict(hello_params, output="all")
+    closure = result["scope"]["hello"]
+    assert closure.signature == {
+        "name": hello_params["text"][0]["def"],
+        "description": hello_params["text"][0]["description"],
+        "type": "function",
+        "parameters": {
+            "type": "object",
+            "properties": {"name": {"type": "string"}},
+            "required": ["name"],
+            "additionalProperties": False,
+        },
+    }
+
+
 hello_stutter = {
     "description": "Repeat the context",
     "text": [