JSON to Dart Converter

Generate strongly-typed Dart classes from your JSON data for Flutter apps.

Class Name

Options Handle Nulls (??)

JSON Input

Dart Code Copied!

How to Use JSON to Dart

1
Paste your JSON object
Drop an API response or any JSON object into the left-hand JSON Input box, or hit Paste Sample to load a working example instantly.
2
Name your Dart class
Type a model name like User or Product into the Class Name field, which defaults to MyModel if you leave it untouched.
3
Toggle null handling
Keep the Handle Nulls (??) checkbox ticked to generate fallback default values, or uncheck it for strict, required-only fields.
4
Click Generate Dart
Press the Generate Dart button to instantly parse your JSON and build a typed class with matching field types in the right pane.
5
Copy the Dart code
Use the Copy button to grab the full class, including its fromJson factory and toJson method, ready to paste into your Flutter project.

Key Features

Automatic Type Detection
Maps JSON values to Dart String, int, double, bool, List, and Map types without any manual setup.
fromJson and toJson
Generates a full factory constructor for parsing and a toJson method for encoding API payloads.
Null-Safe Output
Adds ?? fallback defaults so missing API fields never crash your Flutter app at runtime.
Instant Generation
Converts JSON to a ready-to-use Dart class the moment you click Generate, with no compile step.
One-Click Copy
Copies the entire generated class to your clipboard so you can paste it straight into your model file.
Smart Defaults
Assigns empty strings, zeros, false, and empty collections as sensible defaults per detected type.
Works Offline
Runs entirely in your browser, so you can generate Dart models even with no internet connection.
Flutter Ready
Produces clean class definitions that drop directly into any Flutter or Dart codebase.

Complete Guide to JSON to Dart

What Is JSON to Dart?

JSON to Dart is a free, browser-based code generator that turns a JSON object into a strongly-typed Dart class in a single click. It reads the structure of your JSON, infers the correct Dart type for every field, and writes a complete model class that includes a constructor, a fromJson factory for decoding, and a toJson method for encoding.

For Flutter and Dart developers, this tool removes the most tedious part of working with REST APIs: hand-writing serialization boilerplate. Instead of manually declaring each property and mapping every key, you paste your JSON, name your class, and copy production-ready Dart. Because the entire conversion runs locally in your browser, your data never touches a server.

Why Use a JSON to Dart Converter?

Writing Dart model classes by hand is slow and error-prone. A single mistyped key or wrong type in a fromJson method can cause a runtime crash that is hard to trace. This converter eliminates that risk by deriving types directly from real data.

Saves time: A model that takes ten minutes to type out by hand is generated instantly.
Reduces bugs: Field names and types are copied exactly from your JSON, so typos in key strings disappear.
Enforces type safety: Every field gets a concrete Dart type instead of loose dynamic values scattered through your code.
Handles missing data: With null handling enabled, the generated code falls back to safe defaults when an API omits a field.

The result is cleaner, more predictable code and far less time spent on repetitive plumbing.

Common Use Cases

This tool fits naturally into everyday Flutter development wherever JSON data appears.

Consuming REST APIs: Paste a sample response from an endpoint like a user profile or product listing and instantly get the matching Dart model.
Prototyping new features: When mocking a screen, drop in fake JSON to scaffold the data layer before the backend is finished.
Onboarding to a codebase: Regenerate models from documented API examples to understand a service's data shape quickly.
Migrating from untyped code: Convert ad-hoc Map<String, dynamic> usage into proper classes for safer refactoring.
Building integrations: Generate request and response models for third-party services such as payment gateways or weather APIs.

For example, pasting { "id": 101, "title": "Dart is Awesome", "isActive": true, "score": 98.5 } produces a class with an int id, a String title, a bool isActive, and a double score, complete with serialization.

Best Practices and Tips for Better Results

To get the cleanest output, feed the converter representative JSON. Answer-first: the quality of your generated class depends directly on the quality of your sample data.

Use a complete sample: Include every field you expect, with realistic values, so no property is missed or mistyped.
Provide non-null values: A field set to null is inferred as dynamic, so supply a real value where possible to get a specific type.
Pick a meaningful class name: Replace the default MyModel with a clear name like Order or Article that matches your domain.
Keep null handling on: Leaving the Handle Nulls option enabled protects against incomplete responses from flaky APIs.
Distinguish int from double: A value like 98.5 becomes a double, while 98 becomes an int, so include decimals when a field can be fractional.

Review the generated class once before committing it, especially for nested objects you may want to extract into their own classes.

Supported Formats and Features

The converter accepts any valid JSON object and maps its values to native Dart types. Strings become String, whole numbers become int, decimals become double, true and false become bool, arrays become List, and nested objects become Map<String, dynamic>.

With the Handle Nulls option active, the generated fromJson method applies the ?? operator with sensible defaults: an empty string for text, 0 for integers, 0.0 for doubles, false for booleans, and empty collections for lists and maps. Each generated class ships with a required-parameter constructor, a factory fromJson for decoding incoming data, and a toJson method that returns a map ready to send back to an API.

Professional Applications

In professional Flutter teams, consistent model generation keeps a codebase maintainable as it grows. This tool helps standardize how data classes are written across an app, so every developer produces structurally identical models from the same JSON contract.

It is especially useful during API contract changes. When a backend adds or renames a field, you can regenerate the affected model from the updated response in seconds rather than editing the constructor, factory, and serialization map by hand. Agencies and freelancers juggling many client projects benefit from the speed, turning raw endpoint documentation into a working data layer almost immediately. Because the output is plain, dependency-free Dart, it integrates cleanly with state management approaches like Provider, Riverpod, or Bloc.

Performance Advantages

Conversion happens instantly because all processing runs in your browser using native JavaScript, with no network round-trip and no server queue. The moment you click Generate Dart, the JSON is parsed and the class is written to the output pane.

This client-side approach scales well: large JSON objects with many fields convert just as quickly as small ones, since there is no upload bandwidth to wait on. Once the page has loaded, the tool keeps working even if your connection drops, making it dependable on slow networks, during travel, or behind restrictive corporate firewalls. There are no rate limits and no daily caps, so you can regenerate models as often as your workflow demands.

Security and Privacy

Your JSON never leaves your device. Unlike many online generators that POST your data to a backend, this tool performs every step of the conversion locally in the browser, so sensitive payloads stay entirely on your machine.

That makes it safe to paste real API responses that may contain internal identifiers, tokens, or proprietary data structures without exposing them to a third party. Nothing is logged, stored, or transmitted, and no account or sign-up is required to use it. For developers bound by confidentiality agreements or working with regulated data, this privacy-first design means you can generate Dart models from production-shaped JSON with confidence.

Common Mistakes to Avoid

A few simple habits will spare you confusing output. Answer-first: most issues come from the JSON you paste rather than the generated Dart itself.

Pasting invalid JSON: Trailing commas or single quotes break parsing and produce an error message, so validate your JSON first if generation fails.
Submitting a top-level array: The tool expects an object at the root; a bare list returns a hint to wrap it, so paste a single object instead.
Relying on null fields: Fields whose only sample value is null become loosely typed dynamic, so replace them with real values for proper typing.
Forgetting nested classes: Nested objects are typed as Map<String, dynamic>, so plan to generate separate classes for deep structures you want fully typed.
Leaving the default class name: Shipping a class still called MyModel makes code harder to read, so rename it before copying.

Why Choose ToolWeb for JSON to Dart

Built for speed, privacy, and zero friction — no accounts, no uploads, no cost.

100% Browser-Based

Your JSON is parsed and converted to Dart entirely in your browser, never on a remote server.

No Upload Required

Paste JSON directly into the input box; nothing is uploaded to generate your Dart class.

Instant Processing

Clicking Generate Dart produces a typed class with fromJson and toJson in an instant.

Free Forever

Generate as many Dart models from JSON as you need, with no limits and no cost.

Privacy First

Real API responses with sensitive fields stay on your device and are never logged.

Mobile Friendly

Convert JSON to Dart on a phone or tablet with a responsive, touch-ready interface.

No Registration

Start generating Dart classes immediately without creating an account or signing in.

Works Offline

Once the page loads, you can build Dart models from JSON even with no connection.

Frequently Asked Questions

Common questions about the JSON to Dart — answered.

How do I convert JSON to Dart model classes?

Paste your JSON and the tool generates strongly typed Dart classes with the matching fields, ready to drop into your Flutter or Dart project. It runs in your browser, so it's free and your data stays private. Make sure your JSON is valid first — you can check it with our JSON Formatter.

Does it generate fromJson and toJson methods?

Yes. The generated classes include fromJson and toJson serialization methods so you can parse JSON responses into Dart objects and convert them back to JSON for requests. This saves you from writing repetitive boilerplate by hand for every API model.

Is my JSON sent to a server when generating Dart code?

No. The conversion runs entirely in your browser, so your JSON and the generated Dart code never leave your device. This makes it safe to use with real API responses that may contain sensitive structures or data.

How does it handle nested JSON objects?

Nested objects are turned into separate Dart classes, with the parent class referencing the child class as a typed field. This mirrors your JSON structure in clean, idiomatic Dart so deeply nested API responses become a tidy set of related model classes.

How are JSON arrays and lists handled?

JSON arrays become typed Dart Lists, such as List<String> or List<User> depending on the array's contents. For arrays of objects, the tool generates a model class for the items and types the list accordingly, giving you full type safety when iterating.

What Dart types does the tool infer?

It infers types from your JSON values — strings become String, whole numbers become int, decimals become double, true/false become bool, and objects become custom classes. Because inference is based on the sample you provide, give representative data so optional or nullable fields are detected correctly.

Does it support null safety?

The generated Dart classes are written for modern, null-safe Dart used by current Flutter versions. Review nullable fields based on your API contract, since whether a field can be null depends on your backend, not just the sample JSON you paste in.

Why use generated models instead of dynamic maps in Flutter?

Typed model classes give you compile-time safety, autocomplete, and refactoring support, and they catch field-name typos that a raw Map<String, dynamic> would let slip through to runtime. Generating models also documents your API shape directly in code, making the project easier to maintain.

How do I name the generated classes?

The tool produces a root class you can rename to match your model (for example User, Product, or ApiResponse), and names nested classes from their keys. Pick clear, PascalCase names that reflect what each object represents for clean, readable Flutter code.

Can I use the generated code in any Dart project?

Yes. The output is standard Dart, so it works in Flutter apps as well as server-side Dart, command-line tools, and packages. Just paste the classes into your project and import them where you parse the corresponding JSON.

What if my JSON is invalid?

Invalid JSON can't be reliably converted, so fix any syntax errors first. Paste your data into the JSON Formatter to validate and pinpoint problems like trailing commas or missing brackets, then return here to generate the Dart classes from clean JSON.

Do I need to build a UI from this JSON too?

This tool generates the data models. If you're also converting a web design into Flutter widgets, our HTML to Flutter tool helps turn HTML layouts into Flutter UI code, complementing the models you generate here.

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