About JSON → Kotlin Class

Generate a Kotlin data class from a JSON sample. Part of the DevTools Surf developer suite. Browse more tools in the Converters collection.

Use Cases

• Android developers deserializing API responses with Gson or Moshi
• Backend engineers building Ktor or Spring Boot services
• Data engineers creating type-safe models for JSON event streams
• Mobile teams replacing verbose Java POJOs with concise data classes

Tips

• Nested JSON objects produce nested data classes with proper typing
• Mark nullable fields with Kotlin's ? syntax for safe API parsing
• Copy the generated class directly into your Android Studio project

Fun Facts

• Kotlin data classes automatically generate equals(), hashCode(), toString(), and copy() methods — saving roughly 80 lines of Java boilerplate per class.
• Kotlin was named after Kotlin Island near St. Petersburg, Russia, following the tradition of Java being named after the Indonesian island.
• Google announced Kotlin as a first-class Android language at Google I/O 2017, and by 2020 over 70% of the top 1,000 Android apps used it.

FAQ

data class or regular class?

`data class` by default — gives you equals/hashCode/toString/copy for free and matches Kotlin idioms. Regular class option available for advanced use.

How are nullable fields detected?

Fields that don't appear in every sample record become `Type?` (nullable). Always-present fields are non-nullable. Error-prone with small samples — review the output.

What serialization libraries are supported?

kotlinx.serialization, Jackson, Gson, and Moshi. Pick based on your project; each has slightly different annotation style.

Does it support sealed class hierarchies?

Not auto-detected. If your JSON has a discriminator (e.g. `type: "foo"`), manually create the sealed hierarchy — the tool generates the leaves.