One-click convert JSON data to Kotlin data class definitions with nested classes and nullable types
Zero Dependencies · Works OfflineThe JSON to Kotlin Data Class Converter is a free online developer tool that instantly converts JSON data into Kotlin data class definitions. It automatically identifies JSON field types and maps them to Kotlin types, supporting nested object class generation, Gson/Moshi/Kotlinx Serialization annotations, and nullable type handling. Perfect for Android and Kotlin backend developers who need to quickly generate data class definitions from API responses, dramatically reducing manual coding. All conversion happens locally in your browser — no data is ever uploaded to a server.
1. Paste your JSON data into the input area, or click "Load Example" to try it quickly.
2. Set the class name and conversion options: annotation type, nullable types, integer types.
3. Click "Convert" or use Ctrl+Enter to execute.
4. View the generated Kotlin data class code in the result area below.
5. Click "Copy Code" to copy to clipboard, or download as a .kt file.
When integrating REST APIs, paste the JSON response to instantly generate data classes with Gson annotations, saving manual coding time.
Ktor or Spring Boot developers can quickly generate data classes from request body JSON samples, accelerating API development.
In Kotlin Multiplatform projects, quickly generate platform-specific data class definitions from shared JSON schemas.
When migrating from Java to Kotlin, quickly convert existing JSON models to Kotlin data classes.
Kotlin data classes are specifically designed for holding data, automatically generating equals(), hashCode(), toString(), and copy() methods — more concise and safer than Java POJOs. In Android development, Gson is the most popular JSON library, using @SerializedName to map JSON field names to Kotlin properties. Moshi by Square is a modern alternative with better Kotlin support via @Json. Kotlinx Serialization is JetBrains' official solution with compile-time code generation for better performance, using @SerialName. Nullable types (Type?) are a key Kotlin feature that precisely distinguishes null and non-null values, preventing NPEs.
Yes. Nested objects are automatically generated as separate data classes with their own type names.
With "Nullable types" enabled, null fields generate nullable types (e.g., String?). Disable for non-null types with defaults.
Yes. JSON arrays convert to Kotlin List<T>, where T is inferred from element types.
No. All processing happens locally in your browser. Your data never leaves your device.
Gson @SerializedName, Moshi @Json, and Kotlinx Serialization @SerialName.
Yes. The output follows Kotlin conventions and can be copied directly into a .kt file.