JSON to Dart Converter Online — Generate Class

Writing model classes by hand from a 200-field Flutter API payload wastes hours and is bug-prone — a single typo in a key name silently nulls out a value at runtime. OpenFormatter's converter walks the JSON tree once, generates idiomatic Dart, and runs entirely in your browser so internal API responses never leave your machine.

How to generate Dart classes from JSON — 4 steps

1. Paste a real JSON response. Use a representative sample — type inference quality depends on it. Booleans must be true/false (not 0/1), numbers must be unquoted.
2. Click Convert. The tool emits a Root class plus one separate class per nested object, each with fromJson and toJson methods.
3. Copy and paste into your IDE. Each class is independent — split them into separate .dart files in your lib/models/ folder.
4. Decode the JSON. final root = Root.fromJson(jsonDecode(response.body)); — that is all Dart needs once the class has a fromJson factory.

JSON to Dart type mapping

{
  "id": 42,
  "name": "Ada Lovelace",
  "active": true,
  "score": 98.5,
  "address": { "city": "London" },
  "tags": ["admin", "engineer"]
}

class Root {
  final int id;
  final String name;
  final bool active;
  final double score;
  final Address address;
  final List<String> tags;

  Root({
    required this.id,
    required this.name,
    required this.active,
    required this.score,
    required this.address,
    required this.tags,
  });

  factory Root.fromJson(Map<String, dynamic> json) => Root(
    id: json['id'],
    name: json['name'],
    active: json['active'],
    score: (json['score'] as num).toDouble(),
    address: Address.fromJson(json['address']),
    tags: List<String>.from(json['tags']),
  );

  Map<String, dynamic> toJson() => {
    'id': id,
    'name': name,
    'active': active,
    'score': score,
    'address': address.toJson(),
    'tags': tags,
  };
}

class Address {
  final String city;
  Address({required this.city});
  factory Address.fromJson(Map<String, dynamic> json) =>
      Address(city: json['city']);
  Map<String, dynamic> toJson() => {'city': city};
}

Common use cases

• check_circleGenerating Flutter REST API model classes from a real JSON response
• check_circleBuilding Firestore document models for cloud_firestore reads
• check_circleModelling Firebase Realtime Database snapshots into typed classes
• check_circleProducing GraphQL response shapes for a Flutter app
• check_circleCreating BLoC, Riverpod, or Provider state classes from JSON
• check_circleModelling Dio HTTP client response bodies
• check_circleBuilding shared_preferences or hive serialization classes
• check_circleModelling Stripe, Twilio, or any third-party SaaS webhook payload

Why client-side generation matters

The JSON you paste often contains real customer data, OAuth tokens, signed URLs, or internal field names you do not want indexed by a third-party converter. OpenFormatter generates the Dart entirely in JavaScript on your device — open the Network tab in DevTools and you will see zero requests when you click Convert. Safe for enterprise use, safe behind a corporate proxy, safe when the API contract is itself confidential.