JSON to Dart Class Generator — Free Online Tool

Convert JSON to a Dart class with final fields, a fromJson factory constructor, and a toJson method using AI. Instant, free, no sign-up required.

About JSON to Dart Class Generator — Free Online Tool

JSON to Dart Class converts a JSON object into a typed Dart class with fromJson and toJson factory methods, handling nested objects, nullable fields, and list types automatically. Flutter and Dart developers use it to eliminate the tedious boilerplate of writing data models by hand, reducing errors and saving time when integrating REST APIs.

JSON to Dart Type Mapping

JSON Type	Example Value	Dart Type	Notes
string	"hello"	String	Non-nullable by default; String? when null seen
number (integer)	42	int	Dart uses int for whole numbers
number (float)	3.14	double	Use num if field can be int or double
boolean	true	bool	Maps directly to Dart bool
null	null	dynamic or T?	Field typed as nullable (e.g. String?)
object	{"id":1}	Nested class	New class generated for each nested object
array of strings	["a","b"]	List<String>	Typed list inferred from first element
array of objects	[{"id":1}]	List<ClassName>	Nested class generated; list wraps it
empty array	[]	List<dynamic>	Cannot infer element type from empty array
mixed array	[1,"a"]	List<dynamic>	Heterogeneous arrays fall back to dynamic

JSON Serialization Approaches in Dart/Flutter

Approach	Code Generation	Null Safety	Nested Objects	Best For
Manual fromJson/toJson	No	Manual	Manual	Small projects, learning
json_to_dart tool (this tool)	No (copy-paste)	Yes	Auto-generated	Quick prototyping, one-off models
json_serializable + build_runner	Yes	Yes	Yes	Medium to large projects
freezed + json_serializable	Yes	Yes	Yes (immutable)	Production apps, immutable models
built_value	Yes	Yes	Yes	Enterprise, strict immutability
dart_mappable	Yes	Yes	Yes	Complex generics, custom mapping

Frequently Asked Questions

How does JSON to Dart handle nested objects?

Each nested JSON object generates a separate Dart class with its own fromJson and toJson methods. The parent class holds a typed reference to the child class (e.g. Address address) and delegates serialization to it. This keeps the model hierarchy clean and mirrors the JSON structure exactly.

Does the generated Dart code support null safety?

Yes. Fields whose JSON values are null, or that are absent in the sample, are typed as nullable (e.g. String? or int?). Fields present with non-null values are typed as non-nullable. You should verify nullability against your actual API contract since the generator infers from the sample you provide.

How are JSON arrays converted to Dart?

Arrays of primitives become typed lists such as List<String> or List<int>. Arrays of objects generate a child class and produce List<ChildClass>. Empty arrays fall back to List<dynamic> because the element type cannot be inferred; you should replace dynamic with the correct type manually.

Can I use the generated code directly with Flutter HTTP responses?

Yes. Pass the decoded JSON map from dart:convert to the factory constructor: final obj = MyClass.fromJson(jsonDecode(response.body) as Map<String, dynamic>). The toJson method returns a Map<String, dynamic> suitable for re-encoding with jsonEncode or sending as a request body.

What is the difference between json_to_dart and json_serializable?

json_to_dart (or tools like it) generate ready-to-use class files that you copy into your project — no build step required. json_serializable uses code generation via build_runner to produce .g.dart files that stay in sync automatically when your class changes. For quick one-off models or prototyping, the copy-paste approach is faster; for production codebases with many models, json_serializable is easier to maintain long-term.

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