What is json_serializable in Flutter?

json_serializable is a code generation package that automatically generates fromJson() and toJson() methods for Dart model classes. You annotate your class with @JsonSerializable() and run flutter pub run build_runner build. This eliminates hand-written boilerplate serialization code and reduces the risk of typos in JSON key strings. Combined with the json_annotation package, it supports field renaming, type converters, and null handling customization.