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JSON Toolbox- Free online JSON tools

JSON to Kotlin

Convert JSON to Kotlin data classes online. Types are inferred for nested objects and arrays — and everything runs in your browser.

  • 100% client-side, nothing uploaded
  • Instant results
  • Works offline once loaded
Input JSON

Empty

Kotlin output

Empty

How it works

About this tool

This free online JSON to Kotlin generator turns a sample JSON payload into Kotlin data classes. Paste a representative response, set a root type name, and the tool infers a type for every field — including nested objects and array elements.

Each object becomes a data class with val properties. Optional and nullable values use Kotlin nullable types with a default of null, and a @SerializedName annotation is added when a property name differs from the JSON key.

Helpful for Android or backend Kotlin projects that deserialize with Gson or Moshi and need data classes from a sample payload.

Generation runs entirely in your browser. Your JSON is never uploaded or stored, so it is safe to use with production API responses and payloads that contain sensitive data.

JSON Toolbox processes all data locally in the browser. Nothing is uploaded to a server.

Common questions

Frequently asked questions

How do I convert JSON to Kotlin?
Paste your JSON into the input editor and the generated Kotlin code appears on the right. Set a root type name to control what the top-level type is called, then copy or download the result.
Does it handle nested objects and arrays?
Yes. Nested objects become their own named types, and arrays are typed by their element. When objects in an array have slightly different shapes, their fields are merged and any field missing from some items is marked optional.
What should I know about the generated Kotlin code?
Annotations target common Gson-style naming. If you use kotlinx.serialization, swap annotation styles as needed. Dynamic JSON objects may be better modeled as Map than as a rigid data class.
Is my JSON uploaded anywhere?
No. The Kotlin code is generated locally in your browser. Nothing is sent to a server, logged, or stored — even for large or sensitive payloads.

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