JSON to Kotlin Data Class Generator — Free Online Tool

Add the Kotlin serialization plugin to your build.gradle: `id 'org.jetbrains.kotlin.plugin.serialization' version '1.9.0'` in the plugins block, then add the runtime dependency `implementation 'org.jetbrains.kotlinx:kotlinx-serialization-json:1.6.0'`. The compiler plugin is required — without it, the @Serializable annotation will compile but throw a runtime exception because no serializer is generated.

@SerialName maps a Kotlin property name to a different JSON key, which is essential when the API uses snake_case (e.g., user_id) but you want idiomatic Kotlin camelCase (e.g., userId). Without @SerialName, the property name in your data class must match the JSON key exactly or deserialization returns null/default values. Example: `@SerialName("user_id") val userId: String`.

Fields are generated as nullable when the JSON sample contains a null value for that key, or when the key is missing in some objects within a JSON array. Kotlin enforces null safety at compile time, so the generator marks any field that could legitimately be absent or null as nullable to prevent NullPointerExceptions at runtime. If you know a field will always be present, you can remove the `?` manually.

Yes — nested JSON objects become separate @Serializable data classes that are referenced as property types, and JSON arrays map to List<T> where T is the inferred element type. For deeply nested structures, the generator creates multiple data classes in the same file. kotlinx.serialization handles arbitrary nesting depth as long as all involved classes are annotated with @Serializable.

Use backtick escaping combined with @SerialName: annotate the property with `@SerialName("object")` and name the Kotlin property something idiomatic like `objectData`, or use backticks like `val \`object\`: String` if you must keep the original name. The @SerialName approach is cleaner and more readable. Reserved keywords that commonly appear in JSON include object, class, in, is, val, and return.