Kotlin Data Classes from JSON
Kotlin's data classes are perfect for JSON mapping — they're concise, immutable by default, and come with equals(), hashCode(), and copy() built in. But defining them for every API response is still manual work. This tool generates properly structured data classes from any JSON payload.
Each JSON object becomes a data class with val properties. Types are inferred from values — String, Int, Double, Boolean, or nested class references. All fields are nullable (?) because API responses can be unpredictable and you don't want your app crashing on a missing field.
Android JSON Libraries
The generated data classes work with all major Android JSON libraries. With Gson, they work out of the box. With Moshi, add @JsonClass(generateAdapter = true). With kotlinx.serialization, add @Serializable. The class structure itself is the same regardless of which library you pick.
Retrofit Integration
Retrofit is the most popular Android networking library, and it expects typed response classes. Grab the JSON from your API endpoint (use Postman, curl, or your browser), paste it here, and get Kotlin data classes ready to use as Retrofit response types. Add a converter factory (Gson or Moshi) and your network layer is complete.
Kotlin Multiplatform (KMP)
Building a KMP project that shares networking code between Android and iOS? These data classes work in shared modules too. Pair them with kotlinx.serialization for truly cross-platform JSON handling — same model definitions, same serialization, running on both platforms.
Pro Tips for Kotlin JSON Models
Use default values instead of nullable types where it makes sense. For example,val count: Int = 0 is often better than val count: Int? because you avoid null checks everywhere. Start with the generated nullable classes, then tighten the types as you learn what your API actually guarantees.
Related JSON Tools
For the same API on iOS, generate Swift Codable structs. For Flutter cross-platform apps, try JSON to Dart. Backend Java alternative? Use JSON to Java POJO.