json2freezed

json2freezed generates Dart freezed models from JSON samples.

The preferred way to consume this package is through build_runner, so model files are regenerated as part of the normal Dart or Flutter build workflow. A CLI is also available for one-off generation.

Install

For a Dart project, add json2freezed and the build-time generators as dev dependencies:

dart pub add dev:json2freezed dev:build_runner dev:freezed dev:json_serializable

Generated model files import freezed_annotation and json_annotation. These are peer dependencies of the generated code, so make sure the consuming package installs them directly as regular dependencies:

dart pub add freezed_annotation json_annotation

For a Flutter project, use the same dependency split with flutter pub:

flutter pub add dev:json2freezed dev:build_runner dev:freezed dev:json_serializable
flutter pub add freezed_annotation json_annotation

Build Runner Usage

By default, JSON files under assets/ generate models under lib/generated/:

assets/metro_data_model.json -> lib/generated/metro_data_model.dart

Run:

dart run build_runner build

Configure input and output directories in the consuming package's build.yaml:

targets:
  $default:
    builders:
      json2freezed:
        generate_for:
          - samples/**/*.json
        options:
          input_dir: samples
          output_dir: lib/models

When overriding paths, keep generate_for aligned with input_dir so build_runner knows which JSON files should be primary inputs for the builder.

CLI Install

Install the CLI globally if you want one-off generation outside build_runner:

dart pub global activate json2freezed

Install For Local Development

dart pub get
dart pub global activate --source path .

Usage

Generate from a JSON file:

json2freezed <ClassName> <json-file> [path]

The equivalent flag-based form is:

json2freezed <ClassName> --json-file <file> [--path <dir>] [--overwrite]

Generate from an inline JSON string:

json2freezed <ClassName> --json '<json>' [--path <dir>]

Generate from standard input when neither --json nor --json-file is provided:

cat response.json | json2freezed <ClassName> [--path <dir>]

Options

• <ClassName>: Name of the root Dart class to generate. The class name is normalized to PascalCase.
• <json-file>: Reads the JSON sample from a file.
• [path]: Writes output into the target directory. If omitted, output is written to the current directory.
• --json-file <file>: Reads the JSON sample from a file instead of the positional file argument.
• --json '<json>': Reads the JSON sample from an inline string.
• --path <dir>: Writes output into the target directory instead of the positional path argument.
• --overwrite: Replaces an existing generated file.

Output Naming

The generated Dart class uses PascalCase.

The generated file uses snake_case with a .dart extension. For example:

json2freezed MetroDataModel response.json lib/models

writes:

lib/models/metro_data_model.dart

Generated Model Style

Generated files are expected to include:

• freezed_annotation import
• .freezed.dart and .g.dart part declarations
• nullable constructor fields with @JsonKey(name: ...)
• nested @freezed classes for nested objects and arrays of objects

Run the normal build step in the consuming Dart or Flutter project after generation:

dart run build_runner build