JSON to Dart Class

Generate Dart classes for Flutter from JSON, in your browser.

Class name:

JSON

Dart Class

class Address {
  final String city;
  final String zip;

  const Address({
    required this.city,
    required this.zip,
  });

  factory Address.fromJson(Map<String, dynamic> json) =>
      Address(
    city: json['city'] as String,
    zip: json['zip'] as String,
      );

  Map<String, dynamic> toJson() => {
      'city': city,
      'zip': zip,
      };
}

class User {
  final String name;
  final int age;
  final List<String> skills;
  final Address address;

  const User({
    required this.name,
    required this.age,
    required this.skills,
    required this.address,
  });

  factory User.fromJson(Map<String, dynamic> json) =>
      User(
    name: json['name'] as String,
    age: json['age'] as int,
    skills: (json['skills'] as List<dynamic>).cast<dynamic>(),
    address: Address.fromJson(json['address'] as Map<String, dynamic>),
      );

  Map<String, dynamic> toJson() => {
      'name': name,
      'age': age,
      'skills': skills,
      'address': address.toJson(),
      };
}

Processed in your browser

What it's for

JSON to Dart class for Flutter

Flutter ready

Code compatible with Flutter, json_serializable and freezed. Ready to use with http, dio or Riverpod.

100% private

Your API JSON is processed only in your browser. Sensitive data never leaves your device.

Correct null safety

Automatically detects nullable fields. Required types with required, optional with ? based on the JSON.

Instant

Dart classes ready in milliseconds. No signup, no waiting, no limits.

How it works

Three steps, no hassle

Paste your JSON

Paste the JSON from your API response. The tool infers the correct Dart types for each field.

Dart class generated

You get a Dart class with null safety, factory fromJson() constructor, toJson() method and full typing compatible with json_serializable.

Integrate in Flutter

Copy the generated class to your Flutter project. Works directly with the http package, dio, or any HTTP client.

FAQ

Got questions?

What is the json_serializable package?

json_serializable is the official Dart/Flutter community package for JSON serialization with code generation. Instead of manually writing fromJson() and toJson() methods, you define the class with @JsonSerializable() annotations and the code generator (build_runner) automatically creates the methods. This tool generates code compatible with json_serializable: the class structure, types, and factory fromJson pattern are exactly what build_runner would generate, letting you use the generated code directly or as a starting point for the automatic generation version.

What is the factory fromJson pattern?

The factory fromJson() pattern is the standard in Dart for deserializing JSON. A factory constructor can return an existing instance or create a new one, and in this case receives a Map<String, dynamic> (the result of jsonDecode()) and builds the object. Example: factory User.fromJson(Map<String, dynamic> json) => User(id: json['id'] as int, name: json['name'] as String). The toJson() method does the reverse. This pattern is explicit, type-safe, and easy to test.

How does Dart null safety work?

Dart 2.12 (2021) introduced sound null safety, one of the most important language features. With null safety, types cannot be null by default: String is always a non-null string, while String? can be null. In the JSON context, fields that may be absent or null must be typed as nullable (String?, int?). The required keyword in the constructor indicates a parameter is mandatory and cannot be omitted. This tool automatically detects which JSON fields could be null based on their value and generates the correct typing.

How to integrate generated classes with the API in Flutter?

The typical Flutter flow is: 1) Make the HTTP call with http.get() or dio, 2) Decode the JSON with jsonDecode(response.body), 3) Pass the resulting Map to the factory constructor: final user = User.fromJson(jsonDecode(response.body)). For lists of objects: final users = (jsonDecode(response.body) as List).map((e) => User.fromJson(e)).toList(). With the dio package, you can use interceptors to automatically transform responses. With Riverpod or BLoC, generated classes are used directly as state.

What is the freezed package as an alternative?

freezed is a code generation package for Dart/Flutter that goes beyond json_serializable. It generates immutable classes with: copyWith() method to create modified copies, union/sealed pattern to model states (similar to Kotlin sealed classes), automatic equality and hashCode, and integrated JSON serialization. It is especially popular with Riverpod (the state manager recommended by the Flutter community) for modeling application state. The freezed + Riverpod combination is one of the most adopted architecture patterns in professional Flutter.