JSON to Dart Model (Flutter)

JSON → null-safe Dart classes for Flutter, with fromJson/toJson written out (no build_runner step) and List elements decoded through their own model.

Immutable (final fields + const constructor)

JSON{
  "id": 42,
  "title": "Sunset over Seoul",
  "published": true,
  "rating": 4.6,
  "author": {
    "name": "Ada Lovelace",
    "avatar": null
  },
  "tags": ["travel", "photo"],
  "comments": [
    { "body": "Beautiful shot", "likes": 12 }
  ]
}

Dartclass Root {
  final int id;
  final String title;
  final bool published;
  final double rating;
  final Author author;
  final List<String> tags;
  final List<Comment> comments;

  const Root({
    required this.id,
    required this.title,
    required this.published,
    required this.rating,
    required this.author,
    required this.tags,
    required this.comments,
  });

  factory Root.fromJson(Map<String, dynamic> json) => Root(
        id: json['id'] as int,
        title: json['title'] as String,
        published: json['published'] as bool,
        rating: (json['rating'] as num).toDouble(),
        author: Author.fromJson(json['author'] as Map<String, dynamic>),
        tags: (json['tags'] as List<dynamic>).cast<String>(),
        comments: (json['comments'] as List<dynamic>).map((e) => Comment.fromJson(e as Map<String, dynamic>)).toList(),
      );

  Map<String, dynamic> toJson() => {
        'id': id,
        'title': title,
        'published': published,
        'rating': rating,
        'author': author.toJson(),
        'tags': tags,
        'comments': comments.map((e) => e.toJson()).toList(),
      };
}

class Comment {
  final String body;
  final int likes;

  const Comment({
    required this.body,
    required this.likes,
  });

  factory Comment.fromJson(Map<String, dynamic> json) => Comment(
        body: json['body'] as String,
        likes: json['likes'] as int,
      );

  Map<String, dynamic> toJson() => {
        'body': body,
        'likes': likes,
      };
}

class Author {
  final String name;
  final String? avatar;

  const Author({
    required this.name,
    this.avatar,
  });

  factory Author.fromJson(Map<String, dynamic> json) => Author(
        name: json['name'] as String,
        avatar: json['avatar'] as String?,
      );

  Map<String, dynamic> toJson() => {
        'name': name,
        'avatar': avatar,
      };
}

JSON to Dart Model (Flutter) — Free Online Tool

Generates null-safe Dart model classes from a JSON sample with hand-written fromJson and toJson methods, so Flutter projects need no build_runner step, decoding list elements through their own model, widening ints to double where the JSON shows decimals, and offering immutable final fields with a const constructor.

How to use the JSON to Dart Model (Flutter)

Open the tool above — it runs entirely in your browser, so your input never leaves this page.
Paste or type your input into the field, then press the relevant button (e.g. Encode / Decode, Generate, or Convert).
Copy the result from the output area with the copy button orCtrl/Cmd + C.
No signup, no upload, and no tracking — repeat as often as you need.

Frequently asked questions

Do I need build_runner or json_serializable?

No. The generated classes carry hand-written fromJson factories and toJson methods, so you can paste them into a Flutter project and use them immediately without a code-generation step.

How does it handle Dart null safety?

Fields whose sample value is null become nullable (Type?) and optional in the constructor; every other field is non-nullable and marked required. Numbers that appear with decimals are read as num and converted with .toDouble() so an integer-looking response does not crash the decode.

Are nested lists of objects decoded properly?

Yes. A list whose elements are objects is decoded element by element through that element's own fromJson, rather than being left as List<dynamic>.

Free & private — why use this JSON to Dart Model (Flutter)

The JSON to Dart Model (Flutter) runs 100% client-side in your browser. Your data is never uploaded to a server, no account is required, and the tool is completely free. It works offline once the page has loaded and is part of a growing collection of privacy-first developer utilities.

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