How do I serialize a Flutter model to JSON?

Implement a toJson() method returning Map , then call jsonEncode(model.toJson()) from dart:convert. For HTTP requests with dio, pass model.toJson() directly as the request body — dio serializes Map automatically.

What is the difference between toJson() and jsonEncode() in Dart?

toJson() is a method on your model class that converts the object to a Map — a Dart Map, not a String. jsonEncode() from dart:convert then serializes that Map to a JSON string. You need both: toJson() for the object-to-map step, jsonEncode() for the map-to-string step.

Dart to JSON Converter — toJson & jsonEncode Online

Dart toJson Generator 100% client-side

Paste your Dart class below. The generator extracts fields and builds the toJson() method automatically.

Dart class input

Null safety

Nested objects

toJson() method

jsonEncode() usage

JSON sample output

Dart JSON serialization quick reference

The three patterns you need for every Flutter project.

Object → JSON string

Implement Map<String, dynamic> toJson() on your class, then call jsonEncode(obj.toJson()) from dart:convert. The result is a String you can send as an HTTP body.

JSON string → Object

Call jsonDecode(jsonString) to get a Map<String, dynamic>, then pass it to your MyClass.fromJson(map) factory constructor. Use the JSON to Dart tool to generate fromJson.

With dio HTTP client

Pass model.toJson() directly as the data parameter in dio — dio.post('/endpoint', data: model.toJson()). Dio serializes Map<String, dynamic> automatically, no jsonEncode() needed.

With Firestore

Write: doc.set(model.toJson()). Read: MyClass.fromJson(snap.data()!). The toJson() map maps directly to Firestore document fields — no extra conversion layer needed.

Related tools

All code to json tools

Frequently asked questions

Dart JSON serialization — the most common questions.

How do I add a toJson method to a Dart class?

A toJson() method returns Map<String, dynamic> with each field mapped to its JSON key. For nested objects call their own toJson(). For lists of objects use .map((e) => e.toJson()).toList(). Paste your class above and JSONSwitcher generates the complete implementation.

How do I convert a Dart object to a JSON string?

Two steps: implement toJson() returning Map<String, dynamic>, then call jsonEncode(obj.toJson()) from dart:convert. The result is a String you can use as an HTTP body, write to SharedPreferences, or log for debugging.

What is the difference between toJson() and toMap() in Dart?

They are functionally identical — both return Map<String, dynamic>. toJson() is the more common naming convention and aligns with json_serializable. toMap() is sometimes used when the map isn't specifically for JSON serialization, e.g. for Firestore or SQLite. Use whichever matches your team's convention.

How do I handle nullable fields in toJson with null safety?

Simply include the nullable field in the map — it will serialize as null in the JSON. For example: 'email': email. If you want to omit null fields from the JSON output entirely, use: if (email != null) 'email': email inside the map using a spread with a conditional, or filter the map after building it.

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