What is JSON to Dart Class Generator?
This tool converts JSON data into Dart classes with null safety, fromJson factory constructors, and toJson methods. It automatically infers Dart types, handles nested objects as separate classes, and supports optional copyWith, toString, and freezed code generation for Flutter development.
How to Use
- Set the root class name and configure options (copyWith, toString, freezed)
- Paste your JSON data into the input area
- Click "Generate Dart Code" and copy the output into your Flutter project
Why Use This Tool?
Tips & Best Practices
- Use realistic sample data — type inference depends on actual values
- Enable copyWith for convenient immutable updates in Flutter state management
- Null values in JSON are mapped to nullable types (T?) with optional constructor parameters
- The freezed option generates code compatible with the freezed package — run build_runner after pasting
- Double values use (json['key'] as num).toDouble() to handle both int and double JSON numbers
Frequently Asked Questions
How are JSON types mapped to Dart?
JSON strings → String, integers → int, floats → double, booleans → bool, null → dynamic (nullable), arrays → List<T>, objects → separate nested classes. Double fields use (json['key'] as num).toDouble() to safely handle both int and double values from JSON.
What is the fromJson factory constructor?
The fromJson factory constructor is a Dart pattern for creating class instances from JSON maps. It is used with json.decode() to parse API responses: final user = User.fromJson(jsonDecode(responseBody));
What does the copyWith method do?
The copyWith method creates a new instance of the class with some fields changed while keeping the rest unchanged. This is essential for immutable state management in Flutter, especially with Bloc/Cubit patterns: final updated = user.copyWith(name: "New Name");
What is freezed?
freezed is a Dart code generation package that simplifies creating immutable data classes. When enabled, this tool generates freezed-compatible code with @freezed annotations. You need to add the freezed and freezed_annotation packages and run flutter pub run build_runner build to generate the implementation.
How are nested objects handled?
Nested JSON objects are converted to separate Dart classes. They are ordered children-first, so nested classes appear before the parent class that references them, ensuring valid Dart code. The fromJson and toJson methods automatically handle nested serialization.
Is my data sent to a server?
No, all processing happens entirely in your browser. Your JSON data never leaves your device.