JSON to Dart (Flutter)

About this tool

Paste a JSON response and get Dart classes ready for a Flutter app. Each object becomes a class with a fromJson factory constructor and a toJson method, nested objects and lists are converted for you, and the code follows Dart's sound null safety: a value that is null or missing in your sample becomes a nullable type such as String?. The classes are plain Dart, so they need no extra package and no build step.

Using the model in Flutter

Decode the response with jsonDecode from dart:convert and pass the map to fromJson. To send data back, call toJson and encode the result with jsonEncode.

import 'dart:convert';
import 'package:http/http.dart' as http;

Future<User> fetchUser() async {
  final res = await http.get(Uri.parse('https://api.example.com/users/1'));
  if (res.statusCode != 200) throw Exception('HTTP ${res.statusCode}');
  return User.fromJson(jsonDecode(res.body) as Map<String, dynamic>);
}

// Dart object back to JSON
final body = jsonEncode(user.toJson());

Null safety

Every Dart 3 project runs with sound null safety, so a model has to say which fields can be null. The converter marks a field nullable when it is null or missing in any item of your sample. If your API isn't consistent, tick All fields nullable and check the values where you use them. Code from converters that ignore null safety won't compile in a current Flutter project.

freezed, json_serializable and quicktype

freezed and json_serializable generate fromJson and toJson with build_runner, and freezed adds copyWith, equality and union types. They suit large apps with many models, at the cost of extra packages, annotations and a build step. quicktype is an open source generator for many languages. The classes made here are plain Dart: paste them in and they work. Tick copyWith if you update models in your state management.

Model or entity?

In clean architecture the class made from JSON is the model in the data layer, and the entity is the plain class your app logic uses. Many apps use the model directly. If you keep both, generate the model here and map it to the entity in your repository. VS Code and Android Studio also have extensions that make Dart classes from JSON inside the editor.

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