Developer Tools
JSON to Dart Converter
Paste any JSON and get a null-safe Dart class with factory fromJson and toJson methods — ready to drop into your Flutter project. OpenToolLab's JSON to Dart converter runs entirely in your browser.
Result
What makes this tool different
Null-safe by default
Optional and nullable fields use Dart's ? syntax, matching sound null safety in modern Dart.
fromJson & toJson
Every class includes a factory fromJson constructor and a toJson method ready for jsonEncode.
Typed lists & nesting
Arrays of objects become typed List<Model> and nested objects become their own classes.
100% in-browser privacy
Code generation runs locally. Your JSON never leaves your browser.
About this tool
JSON to Dart Converter: everything you need to know
Flutter developers spend a surprising amount of time writing model classes. Every API response needs a Dart class, a fromJson factory, and a toJson method — and hand-writing them for large payloads invites typos, wrong casts, and null-safety errors. A JSON to Dart converter eliminates that busywork.
OpenToolLab's converter generates sound null-safe Dart. Optional and nullable fields get the ? type annotation, required fields stay non-nullable, and every class includes a factory fromJson constructor plus a toJson method. The output compiles directly in a modern Flutter project without edits.
Type mapping follows Dart conventions: strings to String, numbers to num (int for whole numbers), booleans to bool, and arrays to typed List<T>. Arrays of objects become List<Model> where Model is its own generated class, and nested objects become nested classes. Casting in fromJson uses the safe as Type pattern that null safety expects.
Because the generator is shared, you can convert the same JSON to Dart, TypeScript, Kotlin, or Swift in one window. That is a real productivity win for teams that mirror their API models across Flutter, web, Android, and iOS clients.
Privacy is a core guarantee. All generation happens locally in your browser using nothing but JavaScript — your API responses never touch a server. Open the DevTools Network tab and you will see zero requests while generating.
The generated code follows the exact pattern Flutter documents for manual model creation, so it fits cleanly into an existing codebase. Drop the class into models/, call Model.fromJson(jsonDecode(raw)) where you receive data, and call toJson() before sending — the pattern is consistent and familiar.
Use it when building a new API client, porting a web model to Flutter, or fixing null-safety warnings. Instead of reading a JSON sample and writing each field by hand, paste it once, generate, and get a complete, compile-ready model with zero server involvement.
OpenToolLab is a completely free JSON to Dart converter with no signup, no account, and no limits. Paste your JSON, generate a null-safe model, and get back to building your app — privately and instantly.
FAQ
JSON to Dart Converter — frequently asked questions
How can I convert JSON to Dart?
Paste your JSON into OpenToolLab's JSON to Dart converter and click Generate code. The tool produces a null-safe Dart class with typed fields, a factory fromJson constructor, and a toJson method — ready to paste into your Flutter project.
How to load a JSON file in Dart?
Use rootBundle.loadString('assets/data.json') in Flutter, then jsonDecode() the string and call Model.fromJson() on the result. The fromJson factory generated by this converter does the mapping for you.
Can I convert a JSON file?
Yes. Paste the contents of your JSON file into the converter and generate a Dart model. You can also keep the same sample and switch to TypeScript, Kotlin, or Swift output from the same window.
How can I use JSON in Flutter?
Decode the raw JSON with jsonDecode() to get a Map<String, dynamic>, then pass it to your model's factory: final user = User.fromJson(jsonDecode(raw)). The factory generated here casts each field to its correct type, including nested models and lists.
How do I convert to JSON?
Call toJson() on your model instance to get a Map<String, dynamic>, then jsonEncode() it to a JSON string. The toJson method generated by this converter handles nested models and lists automatically.
How to convert JSON to object in Flutter?
Use the model class generated by this converter: final obj = Model.fromJson(jsonDecode(raw)). The fromJson factory reads each key from the map and assigns it to the typed field, producing a typed Dart object.
What is {} in JSON?
{} is an empty JSON object. If the converter meets an empty object it generates an empty or generic class. Paste a richer sample with real fields to get a fully typed model.
How to convert JSON to string in Flutter?
Use jsonEncode(yourObject.toJson()) where toJson() returns the Map<String, dynamic> representation. The converter generates this method, so encoding a model back to a JSON string is a single call.
Can I convert a JSON to Excel?
For tabular data, OpenToolLab also has a JSON to Excel converter that turns an array of objects into a downloadable .xlsx file. For Dart models, use this JSON to Dart converter to generate typed classes instead.
What is a .JSON file?
A .json file contains JavaScript Object Notation — a text format for structured data using objects, arrays, strings, numbers, and booleans. APIs return JSON, and this converter turns a JSON file's contents into a typed Dart model.
Can I convert JSON to text?
Yes — JSON is already text. The practical conversions are to code (Dart models here), to Excel, to YAML, or to formatted/pretty JSON, all of which OpenToolLab offers as separate client-side tools.
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