JSON to Dart Converter

Paste a JSON object and get Dart classes for Flutter or Dart projects — including `fromJson` factory constructors and `toJson` methods.

Last updated: May 27, 2026

Root class: Final fieldsNullable (T?)fromJson / toJson methods

JSON Input

Generated Dart Classes

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

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

  factory Root.fromJson(Map<String, dynamic> json) {
    return Root(
    userid: json['userId'] as int?,
    name: json['name'] as String?,
    active: json['active'] as bool?,
    score: json['score'] as double?,
    address: json['address'] == null ? null : Address.fromJson(json['address'] as Map<String, dynamic>),
    tags: (json['tags'] as List<dynamic>?)?.cast<String>(),
    );
  }

  Map<String, dynamic> toJson() {
    return {
    'userId': userid,
    'name': name,
    'active': active,
    'score': score,
    'address': address?.toJson(),
    'tags': tags,
    };
  }
}

class Address {
  final String? city;
  final String? zip;

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

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

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

Client-Side Processing

Input Data Stays on Device

Instant Local Execution

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What is JSON to Dart Converter?

Flutter and Dart developers typically write a model class per JSON response, with a `fromJson` factory constructor for deserialization and a `toJson` method for serialization. Writing both directions by hand is mechanical work that scales poorly with the number of endpoints.

This tool generates the full pattern: field declarations with inferred types, a constructor with named parameters, a `fromJson(Map<String, dynamic>)` factory, and a `toJson()` method that mirrors the field names back to a map. Nested objects produce their own classes with their own conversion methods, so deeply nested API responses come out fully typed.

How to Use JSON to Dart Converter

Paste a JSON object (root must be an object).

Set the root class name.

Toggle final fields, nullable types, and fromJson/toJson generation.

Copy the generated classes into your project.

Common Use Cases

Generating Flutter model classes from REST API responses.
Bootstrapping data classes for json_serializable migration.
Quick scaffolding for a Dart CLI that consumes JSON.
Producing a starting point that you refine with package:freezed or similar.

Example Input and Output

A flat JSON object generates a Dart class with fromJson and toJson.

JSON input

{ "userId": 42, "name": "Alice", "active": true }

Generated Dart class

class Root {
  final int? userId;
  final String? name;
  final bool? active;

  Root({this.userId, this.name, this.active});

  factory Root.fromJson(...) { ... }
  Map<String, dynamic> toJson() { ... }
}

Privacy

All conversion happens in your browser. No JSON is sent to a server.

Lists of primitives

List<int>, List<String>, etc. use .cast<T>() in fromJson to safely convert from List<dynamic>. List<NestedClass> uses .map((e) => NestedClass.fromJson(e)).toList().

Frequently Asked Questions

Why are fields nullable by default?

JSON values can be missing, and Dart sound null safety requires explicit nullability. Disabling "Nullable" produces non-nullable fields with required constructor parameters — useful when you trust the API to always return every key.

fromJson / toJson or freezed / json_serializable?

This tool produces hand-written conversion code. For complex projects, consider freezed + json_serializable for code generation and value equality. The classes here are a good starting point to migrate from.

How are int vs double distinguished?

Number.isInteger checks the input value: a whole number becomes int, a decimal becomes double. If you need explicit num to accept both, change manually.

Does this send my JSON anywhere?

No. All generation happens locally in your browser.