JSON to Dart Class Converter

From a JSON sample to a Dart class

The output is a class of final fields with a constructor whose parameters are all required named arguments. That shape is deliberate: it is what sound null safety pushes you toward, and it is the shape json_serializable and freezed expect to decorate. What it does not write is fromJson and toJson, because how you decode is a project decision rather than something a sample payload can answer.

What one sample can and cannot tell it

• Nullability is inferred, not known. Dart has been non-nullable by default since 2.12, so every field arrives non-nullable. Anything the server may omit or send as null needs a ? adding by hand.
• A JSON null carries no type information at all, so it becomes dynamic. That is the honest reading of the sample and almost never the type you want to ship.
• A nested object becomes its own class named after its key, and the parent holds a reference to it rather than an inline map.
• A list is typed from its first element. List<String> from a list of strings is right; a list mixing objects and nulls needs List<dynamic> or a hand-written union.
• Integer and double are told apart by whether the sample value had a fractional part. A price that happened to be 10 infers int and will throw the first time the API sends 10.5. Widen it to double or num.

Building the same model on the other side of a cross-platform app? JSON to Kotlin and JSON to Swift take the same payload, and JSON to TypeScript covers the web client.