JSON to Dart Class Generator (Flutter)

Turn JSON into null-safe Dart model classes for Flutter with fromJson/toJson, or json_serializable annotations. Nested classes and lists included.

Dart code

class User {
  final int id;
  final String name;
  final String email;
  final bool isActive;
  final double balance;
  final DateTime createdAt;
  final List<String> tags;
  final Address address;
  final List<Order> orders;
  final dynamic manager;

  const User({
    required this.id,
    required this.name,
    required this.email,
    required this.isActive,
    required this.balance,
    required this.createdAt,
    required this.tags,
    required this.address,
    required this.orders,
    this.manager,
  });

  factory User.fromJson(Map<String, dynamic> json) => User(
        id: json['id'] as int,
        name: json['name'] as String,
        email: json['email'] as String,
        isActive: json['is_active'] as bool,
        balance: (json['balance'] as num).toDouble(),
        createdAt: DateTime.parse(json['created_at'] as String),
        tags: (json['tags'] as List<dynamic>).map((e) => e as String).toList(),
        address: Address.fromJson(json['address'] as Map<String, dynamic>),
        orders: (json['orders'] as List<dynamic>).map((e) => Order.fromJson(e as Map<String, dynamic>)).toList(),
        manager: json['manager'],
      );

  Map<String, dynamic> toJson() => {
        'id': id,
        'name': name,
        'email': email,
        'is_active': isActive,
        'balance': balance,
        'created_at': createdAt.toIso8601String(),
        'tags': tags,
        'address': address.toJson(),
        'orders': orders.map((e) => e.toJson()).toList(),
        'manager': manager,
      };
}

class Address {
  final String street;
  final String city;

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

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

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

class Order {
  final String orderId;
  final double total;
  final int items;
  final String? coupon;

  const Order({
    required this.orderId,
    required this.total,
    required this.items,
    this.coupon,
  });

  factory Order.fromJson(Map<String, dynamic> json) => Order(
        orderId: json['order_id'] as String,
        total: (json['total'] as num).toDouble(),
        items: json['items'] as int,
        coupon: json['coupon'] as String?,
      );

  Map<String, dynamic> toJson() => {
        'order_id': orderId,
        'total': total,
        'items': items,
        'coupon': coupon,
      };
}

Classes generated

dynamic is used where every sample was null or where samples mix different kinds of values — replace it with the real type once you know it.

A number written as 10.0 is read as a whole number, so a field whose samples are all like that becomes int — include one sample with a fraction to get double.

My tools →

Flutter apps decode JSON into Dart model classes, and writing them by hand — fields, a constructor, fromJson and toJson — is slow and easy to get wrong. Paste a sample API response and get null-safe Dart classes: nested objects become their own classes, arrays become List<T>, fields that are null or missing in some samples become nullable (T?), and snake_case keys become camelCase fields that still read the right JSON key. Choose hand-written fromJson/toJson with no packages, or json_serializable annotations for code generation.

How to use this tool

Paste a representative JSON sample — an array with several items gives the most accurate types.
Enter the root class name.
Pick hand-written fromJson/toJson, json_serializable or fields only.
Decide whether fields are nullable only when needed or always, and whether ISO date strings become DateTime.
Copy the code into a .dart file (for json_serializable, run build_runner).

Formula

whole number → int · fraction → double · true/false → bool · text → String · ISO date → DateTime · [ … ] → List<T> · { … } → class

Values seen at the same place are merged: int and double become double (read through num, so a JSON 1 does not fail the cast), mixed kinds become dynamic. A field that is null in some sample or missing from some array item is nullable. Identical object shapes share one class; list item classes are named from the singular of the key (orders → Order). Names that clash with Dart keywords or dart:core types get a suffix (class → classValue, Map → MapModel).

Example

The sample user gives three classes. User has final int id, String name, String email, bool isActive (from is_active), double balance, DateTime createdAt, List<String> tags, Address address, List<Order> orders and dynamic manager (null in the sample). Order has String orderId, double total (59.9 and 12 merge to double), int items and String? coupon — nullable because only the second order has one. fromJson reads json['order_id'], and toJson writes createdAt with toIso8601String().

Frequently asked questions

Hand-written or json_serializable?

Hand-written fromJson/toJson needs no packages and no build step, which suits small models. json_serializable generates the same code from annotations with build_runner; it is easier to maintain when models change often.

Why is a field typed dynamic?

Every sample was null, or the samples mix kinds such as numbers and text. Paste a sample with a real value, or set the type by hand.

Why does a double field use (json['x'] as num).toDouble()?

JSON does not distinguish 12 from 12.0, so jsonDecode returns an int for whole numbers. Casting straight to double would throw; going through num accepts both.

Is my JSON uploaded?

No. The classes are generated in your browser.

Sources

Last updated: 2026-11-08

Page address with these inputs: https://kakao.mobile/tools/json-to-dart-pojo-generator/

Cite or embed this tool

APA

kakaoCalc. (2026, November 8). JSON to Dart Class Generator (Flutter). https://kakao.mobile/tools/json-to-dart-pojo-generator/

MLA

“JSON to Dart Class Generator (Flutter).” kakaoCalc, 8 Nov. 2026, kakao.mobile/tools/json-to-dart-pojo-generator/.

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JSON to Dart Class Generator (Flutter)

How to use this tool

Formula

Example

Frequently asked questions

Sources

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