diff --git a/examples/tutorial/type_list.pdl b/examples/tutorial/type_list.pdl
index 4c19c0eca..270d37af1 100644
--- a/examples/tutorial/type_list.pdl
+++ b/examples/tutorial/type_list.pdl
@@ -2,5 +2,3 @@
 description: test
 spec: {"list": {"minItems": 0, "maxItems": 0, "str": {}}}
 data: ["hello", "world"]
-  
-  
\ No newline at end of file
diff --git a/pdl-live-react/src/pdl_ast.d.ts b/pdl-live-react/src/pdl_ast.d.ts
index 1bca4fc79..bf4cfa320 100644
--- a/pdl-live-react/src/pdl_ast.d.ts
+++ b/pdl-live-react/src/pdl_ast.d.ts
@@ -40,6 +40,38 @@ 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
+  | ObjPdlType
+  | {
+      [k: string]: PdlTypeType
+    }
+export type Enum = unknown[]
+export type Minlength = number | null
+export type Maxlength = number | null
+export type Pattern = string | null
+export type Multipleof = number | null
+export type Minimum = number | null
+export type Exclusiveminimum = number | null
+export type Maximum = number | null
+export type Exclusivemaximum = number | null
+export type Minimum1 = number | null
+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 Obj = {
+  [k: string]: PdlTypeType
+} | null
 /**
  * Documentation associated to the block.
  *
@@ -168,9 +200,6 @@ export type Parser =
   | RegexParser
   | null
 export type Description21 = string | null
-export type Spec21 = {
-  [k: string]: unknown
-} | null
 export type Pdl =
   | boolean
   | number
@@ -198,9 +227,6 @@ export type Pdl =
   | EmptyBlock
   | null
 export type Description22 = string | null
-export type Spec22 = {
-  [k: string]: unknown
-} | null
 export type Regex = string
 export type Mode = "search" | "match" | "fullmatch" | "split" | "findall"
 /**
@@ -2597,7 +2623,7 @@ export type Kind20 = "function"
  *
  */
 export type Function = {
-  [k: string]: unknown
+  [k: string]: PdlTypeType
 } | null
 /**
  * Body of the function
@@ -2661,7 +2687,11 @@ export type PdlBlock =
  */
 export interface FunctionBlock {
   description?: Description
-  spec?: Spec
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs
   def?: Def24
   contribute?: Contribute20
@@ -2679,12 +2709,82 @@ export interface FunctionBlock {
   return: Return
 }
 /**
- * Type specification of the result of the block.
- *
+ * Enumerated type.
+ */
+export interface EnumPdlType {
+  enum: Enum
+}
+/**
+ * String type.
  */
-export interface Spec {
+export interface StrPdlType {
+  str: StrPdlTypeConstraints | null
+}
+/**
+ * Constraints on string type.
+ */
+export interface StrPdlTypeConstraints {
+  minLength?: Minlength
+  maxLength?: Maxlength
+  pattern?: Pattern
+}
+/**
+ * Float type.
+ */
+export interface FloatPdlType {
+  float: FloatPdlTypeConstraints | null
+}
+/**
+ * Constraints on float type.
+ */
+export interface FloatPdlTypeConstraints {
+  multipleOf?: Multipleof
+  minimum?: Minimum
+  exclusiveMinimum?: Exclusiveminimum
+  maximum?: Maximum
+  exclusiveMaximum?: Exclusivemaximum
+}
+/**
+ * Integer type.
+ */
+export interface IntPdlType {
+  int: IntPdlTypeConstraints | null
+}
+/**
+ * Constraints on integer type.
+ */
+export interface IntPdlTypeConstraints {
+  minimum?: Minimum1
+  exclusiveMinimum?: Exclusiveminimum1
+  maximum?: Maximum1
+  exclusiveMaximum?: Exclusivemaximum1
+}
+/**
+ * List type.
+ */
+export interface ListPdlType {
+  list: List
+}
+/**
+ * Constraints on list type.
+ */
+export interface ListPdlTypeConstraints {
+  minItems?: Minitems
+  maxItems?: Maxitems
   [k: string]: unknown
 }
+/**
+ * Optional type.
+ */
+export interface OptionalPdlType {
+  optional: PdlTypeType
+}
+/**
+ * Optional type.
+ */
+export interface ObjPdlType {
+  obj: Obj
+}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -2722,7 +2822,11 @@ export interface Defs {
  */
 export interface CallBlock {
   description?: Description1
-  spec?: Spec1
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs1
   def?: Def23
   contribute?: Contribute19
@@ -2740,13 +2844,6 @@ export interface CallBlock {
   args?: unknown
   pdl__trace?: PdlTrace3
 }
-/**
- * Type specification of the result of the block.
- *
- */
-export interface Spec1 {
-  [k: string]: unknown
-}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -2791,7 +2888,11 @@ export interface Defs1 {
  */
 export interface LitellmModelBlock {
   description?: Description2
-  spec?: Spec2
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs2
   def?: Def22
   contribute?: Contribute18
@@ -2817,13 +2918,6 @@ export interface LitellmModelBlock {
   platform?: Platform1
   parameters?: Parameters1
 }
-/**
- * Type specification of the result of the block.
- *
- */
-export interface Spec2 {
-  [k: string]: unknown
-}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -2861,7 +2955,11 @@ export interface Defs2 {
  */
 export interface GraniteioModelBlock {
   description?: Description3
-  spec?: Spec3
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs3
   def?: Def21
   contribute?: Contribute17
@@ -2889,13 +2987,6 @@ export interface GraniteioModelBlock {
   processor?: Processor
   parameters?: Parameters
 }
-/**
- * Type specification of the result of the block.
- *
- */
-export interface Spec3 {
-  [k: string]: unknown
-}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -2942,7 +3033,11 @@ export interface Defs3 {
  */
 export interface CodeBlock {
   description?: Description4
-  spec?: Spec4
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs4
   def?: Def20
   contribute?: Contribute16
@@ -2959,13 +3054,6 @@ export interface CodeBlock {
   lang: Lang1
   code: Code
 }
-/**
- * Type specification of the result of the block.
- *
- */
-export interface Spec4 {
-  [k: string]: unknown
-}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -3011,7 +3099,11 @@ export interface Defs4 {
  */
 export interface ArgsBlock {
   description?: Description5
-  spec?: Spec5
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs5
   def?: Def19
   contribute?: Contribute15
@@ -3028,13 +3120,6 @@ export interface ArgsBlock {
   lang?: Lang
   args: Args
 }
-/**
- * Type specification of the result of the block.
- *
- */
-export interface Spec5 {
-  [k: string]: unknown
-}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -3074,7 +3159,11 @@ export interface Defs5 {
  */
 export interface GetBlock {
   description?: Description6
-  spec?: Spec6
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs6
   def?: Def18
   contribute?: Contribute14
@@ -3090,13 +3179,6 @@ export interface GetBlock {
   kind?: Kind14
   get: Get
 }
-/**
- * Type specification of the result of the block.
- *
- */
-export interface Spec6 {
-  [k: string]: unknown
-}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -3155,7 +3237,11 @@ export interface Defs6 {
  */
 export interface DataBlock {
   description?: Description7
-  spec?: Spec7
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs7
   def?: Def17
   contribute?: Contribute13
@@ -3172,13 +3258,6 @@ export interface DataBlock {
   data: unknown
   raw?: Raw
 }
-/**
- * Type specification of the result of the block.
- *
- */
-export interface Spec7 {
-  [k: string]: unknown
-}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -3226,7 +3305,11 @@ export interface Defs7 {
  */
 export interface IfBlock {
   description?: Description8
-  spec?: Spec8
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs8
   def?: Def16
   contribute?: Contribute12
@@ -3246,13 +3329,6 @@ export interface IfBlock {
   else?: Else
   if_result?: IfResult
 }
-/**
- * Type specification of the result of the block.
- *
- */
-export interface Spec8 {
-  [k: string]: unknown
-}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -3307,7 +3383,11 @@ export interface Defs8 {
  */
 export interface MatchBlock {
   description?: Description9
-  spec?: Spec9
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs9
   def?: Def11
   contribute?: Contribute11
@@ -3325,13 +3405,6 @@ export interface MatchBlock {
   match: unknown
   with: With1
 }
-/**
- * Type specification of the result of the block.
- *
- */
-export interface Spec9 {
-  [k: string]: unknown
-}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -3378,7 +3451,11 @@ export interface Defs9 {
  */
 export interface RepeatBlock {
   description?: Description10
-  spec?: Spec10
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs10
   def?: Def10
   contribute?: Contribute10
@@ -3401,13 +3478,6 @@ export interface RepeatBlock {
   join?: Join
   pdl__trace?: PdlTrace2
 }
-/**
- * Type specification of the result of the block.
- *
- */
-export interface Spec10 {
-  [k: string]: unknown
-}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -3445,7 +3515,11 @@ export interface Defs10 {
  */
 export interface TextBlock {
   description?: Description11
-  spec?: Spec11
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs11
   def?: Def9
   contribute?: Contribute9
@@ -3462,13 +3536,6 @@ export interface TextBlock {
   kind?: Kind9
   text: Text
 }
-/**
- * Type specification of the result of the block.
- *
- */
-export interface Spec11 {
-  [k: string]: unknown
-}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -3506,7 +3573,11 @@ export interface Defs11 {
  */
 export interface LastOfBlock {
   description?: Description12
-  spec?: Spec12
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs12
   def?: Def8
   contribute?: Contribute8
@@ -3523,13 +3594,6 @@ export interface LastOfBlock {
   kind?: Kind8
   lastOf: Lastof
 }
-/**
- * Type specification of the result of the block.
- *
- */
-export interface Spec12 {
-  [k: string]: unknown
-}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -3567,7 +3631,11 @@ export interface Defs12 {
  */
 export interface ArrayBlock {
   description?: Description13
-  spec?: Spec13
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs13
   def?: Def7
   contribute?: Contribute7
@@ -3584,13 +3652,6 @@ export interface ArrayBlock {
   kind?: Kind7
   array: Array
 }
-/**
- * Type specification of the result of the block.
- *
- */
-export interface Spec13 {
-  [k: string]: unknown
-}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -3628,7 +3689,11 @@ export interface Defs13 {
  */
 export interface ObjectBlock {
   description?: Description14
-  spec?: Spec14
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs14
   def?: Def6
   contribute?: Contribute6
@@ -3645,13 +3710,6 @@ export interface ObjectBlock {
   kind?: Kind6
   object: Object
 }
-/**
- * Type specification of the result of the block.
- *
- */
-export interface Spec14 {
-  [k: string]: unknown
-}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -3689,7 +3747,11 @@ export interface Defs14 {
  */
 export interface MessageBlock {
   description?: Description15
-  spec?: Spec15
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs15
   def?: Def5
   contribute?: Contribute5
@@ -3707,13 +3769,6 @@ export interface MessageBlock {
   name?: Name
   tool_call_id?: ToolCallId
 }
-/**
- * Type specification of the result of the block.
- *
- */
-export interface Spec15 {
-  [k: string]: unknown
-}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -3763,7 +3818,11 @@ export interface Defs15 {
  */
 export interface ReadBlock {
   description?: Description16
-  spec?: Spec16
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs16
   def?: Def4
   contribute?: Contribute4
@@ -3781,13 +3840,6 @@ export interface ReadBlock {
   message?: Message
   multiline?: Multiline
 }
-/**
- * Type specification of the result of the block.
- *
- */
-export interface Spec16 {
-  [k: string]: unknown
-}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -3825,7 +3877,11 @@ export interface Defs16 {
  */
 export interface IncludeBlock {
   description?: Description17
-  spec?: Spec17
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs17
   def?: Def3
   contribute?: Contribute3
@@ -3843,13 +3899,6 @@ export interface IncludeBlock {
   include: Include
   pdl__trace?: PdlTrace1
 }
-/**
- * Type specification of the result of the block.
- *
- */
-export interface Spec17 {
-  [k: string]: unknown
-}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -3887,7 +3936,11 @@ export interface Defs17 {
  */
 export interface ImportBlock {
   description?: Description18
-  spec?: Spec18
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs18
   def?: Def2
   contribute?: Contribute2
@@ -3904,13 +3957,6 @@ export interface ImportBlock {
   import: Import
   pdl__trace?: PdlTrace
 }
-/**
- * Type specification of the result of the block.
- *
- */
-export interface Spec18 {
-  [k: string]: unknown
-}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -3948,7 +3994,11 @@ export interface Defs18 {
  */
 export interface ErrorBlock {
   description?: Description19
-  spec?: Spec19
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs19
   def?: Def1
   contribute?: Contribute1
@@ -3965,13 +4015,6 @@ export interface ErrorBlock {
   msg: Msg
   program: Program1
 }
-/**
- * Type specification of the result of the block.
- *
- */
-export interface Spec19 {
-  [k: string]: unknown
-}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -4009,7 +4052,11 @@ export interface Defs19 {
  */
 export interface EmptyBlock {
   description?: Description20
-  spec?: Spec20
+  /**
+   * Type specification of the result of the block.
+   *
+   */
+  spec?: PdlTypeType | null
   defs?: Defs20
   def?: Def
   contribute?: Contribute
@@ -4024,13 +4071,6 @@ export interface EmptyBlock {
   pdl__is_leaf?: PdlIsLeaf
   kind?: Kind
 }
-/**
- * Type specification of the result of the block.
- *
- */
-export interface Spec20 {
-  [k: string]: unknown
-}
 /**
  * Set of definitions executed before the execution of the block.
  *
@@ -4087,7 +4127,7 @@ export interface Table {
 }
 export interface PdlParser {
   description?: Description21
-  spec?: Spec21
+  spec?: PdlTypeType | null
   pdl: Pdl
 }
 /**
@@ -4095,7 +4135,7 @@ export interface PdlParser {
  */
 export interface RegexParser {
   description?: Description22
-  spec?: Spec22
+  spec?: PdlTypeType | null
   regex: Regex
   mode?: Mode
 }
diff --git a/src/pdl/pdl-schema.json b/src/pdl/pdl-schema.json
index b1ef1079f..b466cea9e 100644
--- a/src/pdl/pdl-schema.json
+++ b/src/pdl/pdl-schema.json
@@ -45,9 +45,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
@@ -415,9 +422,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
@@ -912,9 +926,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
@@ -1372,9 +1393,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
@@ -1850,9 +1878,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
@@ -2218,9 +2253,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
@@ -2546,6 +2588,22 @@
       "title": "EmptyBlock",
       "type": "object"
     },
+    "EnumPdlType": {
+      "additionalProperties": false,
+      "description": "Enumerated type.",
+      "properties": {
+        "enum": {
+          "items": {},
+          "title": "Enum",
+          "type": "array"
+        }
+      },
+      "required": [
+        "enum"
+      ],
+      "title": "EnumPdlType",
+      "type": "object"
+    },
     "ErrorBlock": {
       "additionalProperties": false,
       "description": "Block representing an error generated at runtime.",
@@ -2564,9 +2622,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
@@ -2985,6 +3050,95 @@
       "title": "ErrorBlock",
       "type": "object"
     },
+    "FloatPdlType": {
+      "additionalProperties": false,
+      "description": "Float type.",
+      "properties": {
+        "float": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/FloatPdlTypeConstraints"
+            },
+            {
+              "type": "null"
+            }
+          ]
+        }
+      },
+      "required": [
+        "float"
+      ],
+      "title": "FloatPdlType",
+      "type": "object"
+    },
+    "FloatPdlTypeConstraints": {
+      "additionalProperties": false,
+      "description": "Constraints on float type.",
+      "properties": {
+        "multipleOf": {
+          "anyOf": [
+            {
+              "type": "number"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "default": null,
+          "title": "Multipleof"
+        },
+        "minimum": {
+          "anyOf": [
+            {
+              "type": "number"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "default": null,
+          "title": "Minimum"
+        },
+        "exclusiveMinimum": {
+          "anyOf": [
+            {
+              "type": "number"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "default": null,
+          "title": "Exclusiveminimum"
+        },
+        "maximum": {
+          "anyOf": [
+            {
+              "type": "number"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "default": null,
+          "title": "Maximum"
+        },
+        "exclusiveMaximum": {
+          "anyOf": [
+            {
+              "type": "number"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "default": null,
+          "title": "Exclusivemaximum"
+        }
+      },
+      "title": "FloatPdlTypeConstraints",
+      "type": "object"
+    },
     "FunctionBlock": {
       "additionalProperties": false,
       "description": "Function declaration.",
@@ -3003,9 +3157,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
@@ -3330,7 +3491,9 @@
         "function": {
           "anyOf": [
             {
-              "additionalProperties": true,
+              "additionalProperties": {
+                "$ref": "#/$defs/PdlTypeType"
+              },
               "type": "object"
             },
             {
@@ -3450,9 +3613,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
@@ -3804,9 +3974,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
@@ -4352,9 +4529,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
@@ -4902,9 +5086,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
@@ -5340,9 +5531,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
@@ -5772,6 +5970,83 @@
       "title": "IndependentEnum",
       "type": "string"
     },
+    "IntPdlType": {
+      "additionalProperties": false,
+      "description": "Integer type.",
+      "properties": {
+        "int": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/IntPdlTypeConstraints"
+            },
+            {
+              "type": "null"
+            }
+          ]
+        }
+      },
+      "required": [
+        "int"
+      ],
+      "title": "IntPdlType",
+      "type": "object"
+    },
+    "IntPdlTypeConstraints": {
+      "additionalProperties": false,
+      "description": "Constraints on integer type.",
+      "properties": {
+        "minimum": {
+          "anyOf": [
+            {
+              "type": "number"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "default": null,
+          "title": "Minimum"
+        },
+        "exclusiveMinimum": {
+          "anyOf": [
+            {
+              "type": "number"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "default": null,
+          "title": "Exclusiveminimum"
+        },
+        "maximum": {
+          "anyOf": [
+            {
+              "type": "number"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "default": null,
+          "title": "Maximum"
+        },
+        "exclusiveMaximum": {
+          "anyOf": [
+            {
+              "type": "number"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "default": null,
+          "title": "Exclusivemaximum"
+        }
+      },
+      "title": "IntPdlTypeConstraints",
+      "type": "object"
+    },
     "JoinArray": {
       "additionalProperties": false,
       "properties": {
@@ -5858,9 +6133,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
@@ -6280,6 +6562,60 @@
       "title": "LastOfBlock",
       "type": "object"
     },
+    "ListPdlType": {
+      "additionalProperties": false,
+      "description": "List type.",
+      "properties": {
+        "list": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "$ref": "#/$defs/ListPdlTypeConstraints"
+            }
+          ],
+          "title": "List"
+        }
+      },
+      "required": [
+        "list"
+      ],
+      "title": "ListPdlType",
+      "type": "object"
+    },
+    "ListPdlTypeConstraints": {
+      "additionalProperties": true,
+      "description": "Constraints on list type.",
+      "properties": {
+        "minItems": {
+          "anyOf": [
+            {
+              "type": "integer"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "default": null,
+          "title": "Minitems"
+        },
+        "maxItems": {
+          "anyOf": [
+            {
+              "type": "integer"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "default": null,
+          "title": "Maxitems"
+        }
+      },
+      "title": "ListPdlTypeConstraints",
+      "type": "object"
+    },
     "LitellmModelBlock": {
       "additionalProperties": false,
       "description": "Call an LLM through [the LiteLLM API](https://docs.litellm.ai/).\n\nExample:\n```PDL\n- model: ollama/granite-code:8b\n  parameters:\n    stop: ['!']\n```",
@@ -6298,9 +6634,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
@@ -7251,9 +7594,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
@@ -7807,9 +8157,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
@@ -8254,6 +8611,31 @@
       "title": "MessageBlock",
       "type": "object"
     },
+    "ObjPdlType": {
+      "additionalProperties": false,
+      "description": "Optional type.",
+      "properties": {
+        "obj": {
+          "anyOf": [
+            {
+              "additionalProperties": {
+                "$ref": "#/$defs/PdlTypeType"
+              },
+              "type": "object"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "title": "Obj"
+        }
+      },
+      "required": [
+        "obj"
+      ],
+      "title": "ObjPdlType",
+      "type": "object"
+    },
     "ObjectBlock": {
       "additionalProperties": false,
       "description": "Return the object where the value of each field is defined by a block. If the body of the object is an array, the resulting object is the union of the objects computed by each element of the array.",
@@ -8272,9 +8654,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
@@ -8839,6 +9228,20 @@
       "title": "ObjectPattern",
       "type": "object"
     },
+    "OptionalPdlType": {
+      "additionalProperties": false,
+      "description": "Optional type.",
+      "properties": {
+        "optional": {
+          "$ref": "#/$defs/PdlTypeType"
+        }
+      },
+      "required": [
+        "optional"
+      ],
+      "title": "OptionalPdlType",
+      "type": "object"
+    },
     "OrPattern": {
       "additionalProperties": false,
       "properties": {
@@ -9028,15 +9431,13 @@
         "spec": {
           "anyOf": [
             {
-              "additionalProperties": true,
-              "type": "object"
+              "$ref": "#/$defs/PdlTypeType"
             },
             {
               "type": "null"
             }
           ],
-          "default": null,
-          "title": "Spec"
+          "default": null
         },
         "pdl": {
           "anyOf": [
@@ -9184,6 +9585,55 @@
       "title": "PdlTiming",
       "type": "object"
     },
+    "PdlTypeType": {
+      "anyOf": [
+        {
+          "enum": [
+            "null",
+            "bool",
+            "str",
+            "float",
+            "int",
+            "list",
+            "obj"
+          ],
+          "type": "string"
+        },
+        {
+          "$ref": "#/$defs/EnumPdlType"
+        },
+        {
+          "$ref": "#/$defs/StrPdlType"
+        },
+        {
+          "$ref": "#/$defs/FloatPdlType"
+        },
+        {
+          "$ref": "#/$defs/IntPdlType"
+        },
+        {
+          "$ref": "#/$defs/ListPdlType"
+        },
+        {
+          "items": {
+            "$ref": "#/$defs/PdlTypeType"
+          },
+          "type": "array"
+        },
+        {
+          "$ref": "#/$defs/OptionalPdlType"
+        },
+        {
+          "$ref": "#/$defs/ObjPdlType"
+        },
+        {
+          "additionalProperties": {
+            "$ref": "#/$defs/PdlTypeType"
+          },
+          "type": "object"
+        }
+      ]
+    },
     "PdlUsage": {
       "description": "Internal data structure to record token consumption usage information.",
       "properties": {
@@ -9317,9 +9767,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
@@ -9701,15 +10158,13 @@
         "spec": {
           "anyOf": [
             {
-              "additionalProperties": true,
-              "type": "object"
+              "$ref": "#/$defs/PdlTypeType"
             },
             {
               "type": "null"
             }
           ],
-          "default": null,
-          "title": "Spec"
+          "default": null
         },
         "regex": {
           "title": "Regex",
@@ -9752,9 +10207,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
@@ -10365,6 +10827,71 @@
       "title": "RepeatBlock",
       "type": "object"
     },
+    "StrPdlType": {
+      "additionalProperties": false,
+      "description": "String type.",
+      "properties": {
+        "str": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/StrPdlTypeConstraints"
+            },
+            {
+              "type": "null"
+            }
+          ]
+        }
+      },
+      "required": [
+        "str"
+      ],
+      "title": "StrPdlType",
+      "type": "object"
+    },
+    "StrPdlTypeConstraints": {
+      "additionalProperties": false,
+      "description": "Constraints on string type.",
+      "properties": {
+        "minLength": {
+          "anyOf": [
+            {
+              "type": "integer"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "default": null,
+          "title": "Minlength"
+        },
+        "maxLength": {
+          "anyOf": [
+            {
+              "type": "integer"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "default": null,
+          "title": "Maxlength"
+        },
+        "pattern": {
+          "anyOf": [
+            {
+              "type": "string"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "default": null,
+          "title": "Pattern"
+        }
+      },
+      "title": "StrPdlTypeConstraints",
+      "type": "object"
+    },
     "TextBlock": {
       "additionalProperties": false,
       "description": "Create the concatenation of the stringify version of the result of each block of the list of blocks.",
@@ -10383,9 +10910,16 @@
           "title": "Description"
         },
         "spec": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/PdlTypeType"
+            },
+            {
+              "type": "null"
+            }
+          ],
           "default": null,
-          "description": "Type specification of the result of the block.\n    ",
-          "title": "Spec"
+          "description": "Type specification of the result of the block.\n    "
         },
         "defs": {
           "additionalProperties": {
diff --git a/src/pdl/pdl_ast.py b/src/pdl/pdl_ast.py
index 4afbb7db1..de8c0d34c 100644
--- a/src/pdl/pdl_ast.py
+++ b/src/pdl/pdl_ast.py
@@ -14,11 +14,18 @@
     Union,
 )
 
-from pydantic import BaseModel, BeforeValidator, ConfigDict, Field, RootModel
+from pydantic import (
+    BaseModel,
+    BeforeValidator,
+    ConfigDict,
+    Field,
+    RootModel,
+    TypeAdapter,
+)
 from pydantic.json_schema import SkipJsonSchema
+from typing_extensions import TypeAliasType
 
 from .pdl_lazy import PdlDict, PdlLazy
-from .pdl_schema_utils import pdltype_to_jsonschema
 
 
 def _ensure_lower(value):
@@ -134,6 +141,119 @@ class AnyPattern(Pattern):
 )
 
 
+BasePdlType: TypeAlias = Literal["null", "bool", "str", "float", "int", "list", "obj"]
+
+
+class PdlType(BaseModel):
+    """Common fields for PDL types."""
+
+    model_config = ConfigDict(extra="forbid")
+
+
+class EnumPdlType(PdlType):
+    """Enumerated type."""
+
+    enum: list[Any]
+    """List of allowed values in the type."""
+
+
+class StrPdlTypeConstraints(BaseModel):
+    """Constraints on string type."""
+
+    model_config = ConfigDict(extra="forbid")
+    minLength: Optional[int] = None
+    """Minimal length of the string."""
+    maxLength: Optional[int] = None
+    """Maximal length of the string."""
+    pattern: Optional[str] = None
+    """Regular expression that values of the type must match."""
+
+
+class StrPdlType(PdlType):
+    """String type."""
+
+    str: Optional[StrPdlTypeConstraints]
+
+
+class FloatPdlTypeConstraints(BaseModel):
+    """Constraints on float type."""
+
+    model_config = ConfigDict(extra="forbid")
+    multipleOf: Optional[float] = None
+    minimum: Optional[float] = None
+    exclusiveMinimum: Optional[float] = None
+    maximum: Optional[float] = None
+    exclusiveMaximum: Optional[float] = None
+
+
+class FloatPdlType(PdlType):
+    """Float type."""
+
+    float: Optional[FloatPdlTypeConstraints]
+
+
+class IntPdlTypeConstraints(BaseModel):
+    """Constraints on integer type."""
+
+    model_config = ConfigDict(extra="forbid")
+    minimum: Optional[float] = None
+    exclusiveMinimum: Optional[float] = None
+    maximum: Optional[float] = None
+    exclusiveMaximum: Optional[float] = None
+
+
+class IntPdlType(PdlType):
+    """Integer type."""
+
+    int: Optional[IntPdlTypeConstraints]
+
+
+class ListPdlTypeConstraints(BaseModel):
+    """Constraints on list type."""
+
+    model_config = ConfigDict(extra="allow")
+    minItems: Optional[int] = None
+    maxItems: Optional[int] = None
+
+
+class ListPdlType(PdlType):
+    """List type."""
+
+    list: Union["PdlTypeType", ListPdlTypeConstraints]
+
+
+class OptionalPdlType(PdlType):
+    """Optional type."""
+
+    optional: "PdlTypeType"
+
+
+class ObjPdlType(PdlType):
+    """Optional type."""
+
+    obj: Optional[dict[str, "PdlTypeType"]]
+
+
+PdlTypeType = TypeAliasType(
+    "PdlTypeType",
+    Annotated[
+        "Union[BasePdlType,"  # pyright: ignore
+        "      EnumPdlType,"
+        "      StrPdlType,"
+        "      FloatPdlType,"
+        "      IntPdlType,"
+        "      ListPdlType,"
+        "      list['PdlTypeType'],"
+        "      OptionalPdlType,"
+        "      ObjPdlType,"
+        "      dict[str, 'PdlTypeType']]",
+        Field(union_mode="left_to_right"),
+    ],
+)
+
+pdl_type_adapter = TypeAdapter(PdlTypeType)
+
+
 class Parser(BaseModel):
     """Common fields for all parsers (`parser` field)."""
 
@@ -141,7 +261,7 @@ class Parser(BaseModel):
     description: Optional[str] = None
     """Documentation associated to the parser.
     """
-    spec: Optional[dict[str, Any]] = None
+    spec: Optional[PdlTypeType] = None
     """Expected type of the parsed value.
     """
 
@@ -220,7 +340,7 @@ class Block(BaseModel):
     description: Optional[str] = None
     """Documentation associated to the block.
     """
-    spec: Any = None
+    spec: Optional[PdlTypeType] = None
     """Type specification of the result of the block.
     """
     defs: dict[str, "BlockType"] = {}
@@ -278,7 +398,7 @@ class FunctionBlock(LeafBlock):
     """Function declaration."""
 
     kind: Literal[BlockKind.FUNCTION] = BlockKind.FUNCTION
-    function: Optional[dict[str, Any]]
+    function: Optional[dict[str, PdlTypeType]]
     """Functions parameters with their types.
     """
     returns: "BlockType" = Field(..., alias="return")
@@ -925,33 +1045,6 @@ def __init__(
 DECODING_METHOD = "greedy"
 
 
-def set_structured_decoding_parameters(
-    spec: Any,
-    parameters: Optional[dict[str, Any]],
-) -> dict[str, Any]:
-    if parameters is None:
-        parameters = {}
-
-    if (
-        spec is not None
-        and "response_format" not in parameters
-        and "guided_decoding_backend" not in parameters
-    ):
-        schema = pdltype_to_jsonschema(spec, True)
-
-        parameters["guided_decoding_backend"] = "lm-format-enforcer"
-        parameters["guided_json"] = schema
-        parameters["response_format"] = {
-            "type": "json_schema",
-            "json_schema": {
-                "name": "schema",
-                "schema": schema,
-                "strict": True,
-            },
-        }
-    return parameters
-
-
 def get_default_model_parameters() -> list[dict[str, Any]]:
     """Model-specific defaults to apply"""
     return [
diff --git a/src/pdl/pdl_dumper.py b/src/pdl/pdl_dumper.py
index 95f96d0a6..f30100780 100644
--- a/src/pdl/pdl_dumper.py
+++ b/src/pdl/pdl_dumper.py
@@ -17,17 +17,22 @@
     ContributeValue,
     DataBlock,
     EmptyBlock,
+    EnumPdlType,
     ErrorBlock,
     ExpressionType,
+    FloatPdlType,
     FunctionBlock,
     GetBlock,
     GraniteioModelBlock,
     IfBlock,
     ImportBlock,
     IncludeBlock,
+    IntPdlType,
     JoinText,
     JoinType,
     LastOfBlock,
+    ListPdlType,
+    ListPdlTypeConstraints,
     LitellmModelBlock,
     LitellmParameters,
     LocalizedExpression,
@@ -35,16 +40,20 @@
     MessageBlock,
     ObjectBlock,
     ObjectPattern,
+    ObjPdlType,
+    OptionalPdlType,
     OrPattern,
     ParserType,
     PatternType,
     PdlLocationType,
     PdlParser,
     PdlTiming,
+    PdlTypeType,
     PdlUsage,
     ReadBlock,
     RegexParser,
     RepeatBlock,
+    StrPdlType,
     StructuredBlock,
     TextBlock,
 )
@@ -107,7 +116,7 @@ def block_to_dict(  # noqa: C901
     if block.role is not None:
         d["role"] = block.role
     if block.spec is not None:
-        d["spec"] = block.spec
+        d["spec"] = type_to_dict(block.spec)
     if block.defs is not None:
         d["defs"] = {
             x: block_to_dict(b, json_compatible) for x, b in block.defs.items()
@@ -227,7 +236,10 @@ def block_to_dict(  # noqa: C901
                     block_to_dict(b, json_compatible) for b in block.pdl__trace
                 ]
         case FunctionBlock():
-            d["function"] = block.function
+            if block.function is None:
+                d["function"] = None
+            else:
+                d["function"] = {x: type_to_dict(t) for x, t in block.function.items()}
             d["return"] = block_to_dict(block.returns, json_compatible)
             # if block.scope is not None:
             #     d["scope"] = scope_to_dict(block.scope, json_compatible)
@@ -245,7 +257,10 @@ def block_to_dict(  # noqa: C901
             d["msg"] = block.msg
     if block.def_ is not None:
         d["def"] = block.def_
-    if set(block.contribute) != {ContributeTarget.RESULT, ContributeTarget.CONTEXT}:
+    if block.contribute not in [
+        [ContributeTarget.RESULT, ContributeTarget.CONTEXT],
+        [ContributeTarget.CONTEXT, ContributeTarget.RESULT],
+    ]:
         d["contribute"] = contribute_to_list(block.contribute)
     if block.pdl__result is not None:
         if isinstance(block.pdl__result, FunctionBlock):
@@ -291,6 +306,86 @@ def expr_to_dict(expr: ExpressionType, json_compatible: bool):
     return d
 
 
+def type_to_dict(t: PdlTypeType):
+    d: str | list | dict
+    match t:
+        case "null" | "bool" | "str" | "float" | "int" | "list" | "obj":
+            d = t
+        case EnumPdlType():
+            d = {"enum": t.enum}
+        case StrPdlType():
+            if t.str is None:
+                d = "str"
+            else:
+                cstr: dict = {}
+                if t.str.minLength is not None:
+                    cstr["minLength"] = t.str.minLength
+                if t.str.maxLength is not None:
+                    cstr["maxLength"] = t.str.maxLength
+                if t.str.pattern is not None:
+                    cstr["pattern"] = t.str.pattern
+                d = {"str": cstr}
+        case FloatPdlType():
+            if t.float is None:
+                d = "float"
+            else:
+                cstr = {}
+                if t.float.multipleOf is not None:
+                    cstr["multipleOf"] = t.float.multipleOf
+                if t.float.minimum is not None:
+                    cstr["minimum"] = t.float.minimum
+                if t.float.exclusiveMinimum is not None:
+                    cstr["exclusiveMinimum"] = t.float.exclusiveMinimum
+                if t.float.maximum is not None:
+                    cstr["maximum"] = t.float.maximum
+                if t.float.exclusiveMaximum is not None:
+                    cstr["exclusiveMaximum"] = t.float.exclusiveMaximum
+                d = {"float": cstr}
+        case IntPdlType():
+            if t.int is None:
+                d = "int"
+            else:
+                cstr = {}
+                if t.int.minimum is not None:
+                    cstr["minimum"] = t.int.minimum
+                if t.int.exclusiveMinimum is not None:
+                    cstr["exclusiveMinimum"] = t.int.exclusiveMinimum
+                if t.int.maximum is not None:
+                    cstr["maximum"] = t.int.maximum
+                if t.int.exclusiveMaximum is not None:
+                    cstr["exclusiveMaximum"] = t.int.exclusiveMaximum
+                d = {"int": cstr}
+        case ListPdlType():
+            if t.list is None:
+                d = "list"
+            else:
+                if isinstance(t.list, ListPdlTypeConstraints):
+                    cstr = type_to_dict(t.list.__pydantic_extra__)
+                    if t.list.minItems is not None:
+                        cstr["minItems"] = t.list.minItems
+                    if t.list.maxItems is not None:
+                        cstr["maxItems"] = t.list.maxItems
+                    d = {"list": cstr}
+                else:
+                    d = {"list": type_to_dict(t.list)}
+        case [elem]:
+            d = [type_to_dict(elem)]  # type:ignore
+        case list():
+            assert False, "list must have only one element"
+        case OptionalPdlType():
+            d = {"optional": type_to_dict(t.optional)}
+        case ObjPdlType():
+            if t.obj is None:
+                d = "obj"
+            else:
+                d = {"obj": {x: type_to_dict(t_x) for x, t_x in t.obj.items()}}
+        case dict():
+            d = {x: type_to_dict(t_x) for x, t_x in t.items()}
+        case _:
+            assert False
+    return d
+
+
 def timing_to_dict(timing: PdlTiming) -> dict:
     d: dict = {}
     if timing.start_nanos != 0:
@@ -369,11 +464,13 @@ def parser_to_dict(parser: ParserType) -> str | dict[str, Any]:
         case "json" | "yaml" | "jsonl":
             p = parser
         case RegexParser():
-            p = parser.model_dump()
+            p = parser.model_dump(exclude_unset=True)
         case PdlParser():
             p = {}
-            p["description"] = parser.description
-            p["spec"] = parser.spec
+            if parser.description is not None:
+                p["description"] = parser.description
+            if parser.spec is not None:
+                p["spec"] = type_to_dict(parser.spec)
             p["pdl"] = block_to_dict(parser.pdl, False)
         case _:
             assert False
diff --git a/src/pdl/pdl_interpreter.py b/src/pdl/pdl_interpreter.py
index 14c3f9f53..f2eb67b53 100644
--- a/src/pdl/pdl_interpreter.py
+++ b/src/pdl/pdl_interpreter.py
@@ -70,6 +70,7 @@
     ModelInput,
     ObjectBlock,
     ObjectPattern,
+    ObjPdlType,
     OrPattern,
     ParserType,
     Pattern,
@@ -1923,19 +1924,20 @@ def parse_result(parser: ParserType, text: str) -> JSONReturnType:
                 raise PDLRuntimeParserError(msg) from exc
             if m is None:
                 return None
-            if parser.spec is None:
-                result = list(m.groups())
-            else:
-                current_group_name = ""
-                try:
-                    result = {}
-                    for x in parser.spec.keys():
-                        current_group_name = x
-                        result[x] = m.group(x)
-                    return result
-                except IndexError as exc:
-                    msg = f"No group named {current_group_name} found by {regex} in {text}"
-                    raise PDLRuntimeParserError(msg) from exc
+            match parser.spec:
+                case ObjPdlType(obj=dict() as spec) | (dict() as spec):
+                    current_group_name = ""
+                    try:
+                        result = {}
+                        for x in spec.keys():
+                            current_group_name = x
+                            result[x] = m.group(x)
+                        return result
+                    except IndexError as exc:
+                        msg = f"No group named {current_group_name} found by {regex} in {text}"
+                        raise PDLRuntimeParserError(msg) from exc
+                case _:
+                    result = list(m.groups())
         case RegexParser(mode="split" | "findall"):
             regex = parser.regex
             match parser.mode:
diff --git a/src/pdl/pdl_llms.py b/src/pdl/pdl_llms.py
index 34c0a62a6..5c0db1a0c 100644
--- a/src/pdl/pdl_llms.py
+++ b/src/pdl/pdl_llms.py
@@ -4,7 +4,7 @@
 from concurrent.futures import Future
 from os import environ
 from sys import stderr
-from typing import Any, Callable, Generator, TypeVar
+from typing import Any, Callable, Generator, Optional, TypeVar
 
 import httpx
 from dotenv import load_dotenv
@@ -15,9 +15,10 @@
     LitellmModelBlock,
     ModelInput,
     PDLRuntimeError,
-    set_structured_decoding_parameters,
+    PdlTypeType,
 )
 from .pdl_lazy import PdlConst, PdlLazy, lazy_apply
+from .pdl_schema_utils import pdltype_to_jsonschema
 from .pdl_utils import remove_none_values_from_message
 
 # Load environment variables
@@ -181,6 +182,33 @@ def generate_text_stream(
         return result
 
 
+def set_structured_decoding_parameters(
+    spec: Optional[PdlTypeType],
+    parameters: Optional[dict[str, Any]],
+) -> dict[str, Any]:
+    if parameters is None:
+        parameters = {}
+
+    if (
+        spec is not None
+        and "response_format" not in parameters
+        and "guided_decoding_backend" not in parameters
+    ):
+        schema = pdltype_to_jsonschema(spec, True)
+
+        parameters["guided_decoding_backend"] = "lm-format-enforcer"
+        parameters["guided_json"] = schema
+        parameters["response_format"] = {
+            "type": "json_schema",
+            "json_schema": {
+                "name": "schema",
+                "schema": schema,
+                "strict": True,
+            },
+        }
+    return parameters
+
+
 MapInputT = TypeVar("MapInputT")
 MapOutputT = TypeVar("MapOutputT")
 
diff --git a/src/pdl/pdl_schema_utils.py b/src/pdl/pdl_schema_utils.py
index 9920b0c46..402c38a76 100644
--- a/src/pdl/pdl_schema_utils.py
+++ b/src/pdl/pdl_schema_utils.py
@@ -1,6 +1,19 @@
 import warnings
 from typing import Any, Optional
 
+from .pdl_ast import (
+    EnumPdlType,
+    FloatPdlType,
+    IntPdlType,
+    ListPdlType,
+    ListPdlTypeConstraints,
+    ObjPdlType,
+    OptionalPdlType,
+    PdlTypeType,
+    StrPdlType,
+    pdl_type_adapter,
+)
+
 json_types_convert = {
     "string": str,
     "boolean": bool,
@@ -29,59 +42,96 @@ def convert_to_json_type(a_type):
 }
 
 
-def pdltype_to_jsonschema(  # pylint: disable=too-many-return-statements
-    pdl_type: str | dict[str, Any] | list, additional_properties: bool
+def pdltype_to_jsonschema(
+    pdl_type: Optional[PdlTypeType], additional_properties: bool
 ) -> dict[str, Any]:
+    schema: dict[str, Any]
     match pdl_type:
-        case {"enum": choices}:
-            return {"enum": choices}
         case None:
-            return {"type": "null"}
-        case "bool" | "str" | "float" | "int" | "list" | "obj":
-            return {"type": _PDLTYPE_TO_JSONSCHEMA_NAME[pdl_type]}
-        case {"str": dict() as details}:
-            return {"type": "string", **details}
-        case {"float": dict() as details}:
-            return {"type": "number", **details}
-        case {"int": dict() as details}:
-            return {"type": "integer", **details}
-        case {"list": str() as type_name}:
-            return {
+            schema = {}  # Any type
+        case "null" | "bool" | "str" | "float" | "int" | "list" | "obj":
+            schema = {"type": _PDLTYPE_TO_JSONSCHEMA_NAME[pdl_type]}
+        case EnumPdlType(enum=choices):
+            schema = {"enum": choices}
+        case StrPdlType(str=None):
+            schema = {"type": "string"}
+        case StrPdlType(str=constraints):
+            if constraints is None:
+                details = {}
+            else:
+                details = constraints.model_dump(exclude_defaults=True)
+            schema = {"type": "string", **details}
+        case FloatPdlType(float=constraints):
+            if constraints is None:
+                details = {}
+            else:
+                details = constraints.model_dump(exclude_defaults=True)
+            schema = {"type": "number", **details}
+        case IntPdlType(int=constraints):
+            if constraints is None:
+                details = {}
+            else:
+                details = constraints.model_dump(exclude_defaults=True)
+            schema = {"type": "integer", **details}
+        case ListPdlType(list=ListPdlTypeConstraints() as cstr):
+            items_type = pdl_type_adapter.validate_python(cstr.__pydantic_extra__)
+            details = {}
+            if cstr.minItems is not None:
+                details["minItems"] = cstr.minItems
+            if cstr.maxItems is not None:
+                details["maxItems"] = cstr.maxItems
+            schema = {
                 "type": "array",
-                "items": pdltype_to_jsonschema(type_name, additional_properties),
+                "items": pdltype_to_jsonschema(items_type, additional_properties),
+                **details,
             }
-        case {"list": dict() as details}:
-            ikws = ["enum", *_PDLTYPE_TO_JSONSCHEMA_NAME.keys()]
-            items_details = {k: v for k, v in details.items() if k in ikws}
-            if len(items_details) != 1:
-                raise ValueError(f"invalid PDL type {pdl_type}")
-            other_details = {k: v for k, v in details.items() if k not in ikws}
-            return {
+        case ListPdlType(list=items_type):
+            schema = {
                 "type": "array",
-                "items": pdltype_to_jsonschema(items_details, additional_properties),
-                **other_details,
+                "items": pdltype_to_jsonschema(items_type, additional_properties),
             }
+        # case {"list": dict() as details}:
+        #     ikws = ["enum", *_PDLTYPE_TO_JSONSCHEMA_NAME.keys()]
+        #     items_details = {k: v for k, v in details.items() if k in ikws}
+        #     if len(items_details) != 1:
+        #         raise ValueError(f"invalid PDL type {pdl_type}")
+        #     other_details = {k: v for k, v in details.items() if k not in ikws}
+        #     return {
+        #         "type": "array",
+        #         "items": pdltype_to_jsonschema(items_details, additional_properties),
+        #         **other_details,
+        #     }
         case list() as type_list:
             if len(type_list) != 1:
                 raise ValueError(f"invalid PDL type {pdl_type}")
-            return {
+            schema = {
                 "type": "array",
                 "items": pdltype_to_jsonschema(type_list[0], additional_properties),
             }
-        case {"obj": dict() as pdl_props}:
-            return get_json_schema_object(pdl_props, additional_properties)
+        case OptionalPdlType(optional=t):
+            t_schema = pdltype_to_jsonschema(t, additional_properties)
+            schema = {"anyOf": [t_schema, "null"]}
+        case ObjPdlType(obj=pdl_props):
+            if pdl_props is None:
+                schema = {"type": "object"}
+            else:
+                schema = get_json_schema_object(pdl_props, additional_properties)
         case dict() as pdl_props:
             return get_json_schema_object(pdl_props, additional_properties)
-    raise ValueError(f"invalid PDL type {pdl_type}")
+        case _:
+            raise ValueError(f"invalid PDL type {pdl_type}")
+    return schema
 
 
-def get_json_schema_object(pdl_props: dict, additional_properties) -> dict[str, Any]:
+def get_json_schema_object(
+    pdl_props: dict[str, PdlTypeType], additional_properties
+) -> dict[str, Any]:
     props = {}
     required = []
     for name, prop_type in pdl_props.items():
-        if isinstance(prop_type, dict) and "optional" in prop_type:
+        if isinstance(prop_type, OptionalPdlType):
             props[name] = pdltype_to_jsonschema(
-                prop_type["optional"], additional_properties
+                prop_type.optional, additional_properties
             )
         else:
             props[name] = pdltype_to_jsonschema(prop_type, additional_properties)
@@ -98,10 +148,12 @@ def get_json_schema_object(pdl_props: dict, additional_properties) -> dict[str,
 
 
 def get_json_schema(
-    params: dict[str, Any], additional_properties
+    params: dict[str, PdlTypeType], additional_properties
 ) -> Optional[dict[str, Any]]:
     try:
-        result = pdltype_to_jsonschema({"obj": params}, additional_properties)
+        result = pdltype_to_jsonschema(
+            ObjPdlType.model_validate({"obj": params}), additional_properties
+        )
         return result
     except ValueError as e:
         warnings.warn(e.args[0])
diff --git a/src/pdl/pdl_schema_validator.py b/src/pdl/pdl_schema_validator.py
index b29f14161..160a1e8c4 100644
--- a/src/pdl/pdl_schema_validator.py
+++ b/src/pdl/pdl_schema_validator.py
@@ -1,7 +1,7 @@
 # pylint: disable=import-outside-toplevel
 from typing import Any, Optional
 
-from .pdl_ast import FunctionBlock
+from .pdl_ast import FunctionBlock, PdlTypeType
 from .pdl_location_utils import get_loc_string
 from .pdl_schema_error_analyzer import analyze_errors
 from .pdl_schema_utils import get_json_schema, pdltype_to_jsonschema
@@ -35,7 +35,7 @@ def type_check_args(
     return type_check(args_copy, schema, loc)
 
 
-def type_check_spec(result: Any, spec: str | dict[str, Any] | list, loc) -> list[str]:
+def type_check_spec(result: Any, spec: Optional[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_type_checking.py b/tests/test_type_checking.py
index e25c5e809..b82e5823d 100644
--- a/tests/test_type_checking.py
+++ b/tests/test_type_checking.py
@@ -2,12 +2,18 @@
 import yaml
 
 from pdl.pdl import exec_dict
+from pdl.pdl_ast import pdl_type_adapter
 from pdl.pdl_interpreter import PDLRuntimeError
+from pdl.pdl_parser import PDLParseError
 from pdl.pdl_schema_utils import pdltype_to_jsonschema
 
 _PDLTYPE_TO_JSONSCHEMA_TESTS = [
     {
         "pdl_type": "null",
+        "json_schema": {},
+    },
+    {
+        "pdl_type": '"null"',
         "json_schema": {"type": "null"},
     },
     {
@@ -139,7 +145,11 @@
 
 def test_pdltype_to_jsonschema():
     for t in _PDLTYPE_TO_JSONSCHEMA_TESTS:
-        pdl_type = yaml.safe_load(t["pdl_type"])
+        t_data = yaml.safe_load(t["pdl_type"])
+        if t_data is None:
+            pdl_type = None
+        else:
+            pdl_type = pdl_type_adapter.validate_python(t_data)
         json_schema = pdltype_to_jsonschema(pdl_type, False)
         assert json_schema == t["json_schema"]
 
@@ -314,7 +324,7 @@ def test_function_call7():
 
 
 def test_function_call8():
-    with pytest.raises(PDLRuntimeError):
+    with pytest.raises(PDLParseError):
         exec_dict(function_call8)