{ } JSON Workbench0 network requests. Check DevTools

"JSON to Kotlin":{ }

Paste a JSON sample and get clean Kotlin data classes. Nested objects become named types, arrays become typed collections, and nullable fields are handled. Powered by quicktype's inference engine running 100% in your browser: zero network requests, so real API payloads stay on your machine.

What is a JSON to Kotlin converter?

Hand-writing data classes for an API response is slow and error-prone. This tool infers Kotlin data classes from a JSON sample: nested objects become named types, arrays become typed collections, and null/missing values become optional fields. It runs quicktype's inference engine entirely in your browser, so real API payloads (often containing user data or credentials) never leave your machine.

Kotlin mapping notes

  • Kotlin data classes give you equals/hashCode/copy/toString for free.
  • JSON integers map to Long and decimals to Double; nullable or missing fields become T?.
  • The classes are annotation-free, so they drop straight into a kotlinx.serialization, Moshi, or Jackson setup.

How to use

  1. Paste a JSON sample (an API response works well) into the Input pane.
  2. Generated Kotlin data classes appear instantly. Nested objects become their own named types.
  3. Non-standard JSON (single quotes, trailing commas, comments) is auto-repaired first.
  4. Copy the code into your project.

Examples

JSON → Kotlin data classes

Input
{
  "id": 42,
  "name": "workbench",
  "owner": { "email": "[email protected]", "active": true }
}
Output
data class Root (
    val id: Long,
    val name: String,
    val owner: Owner
)

data class Owner (
    val email: String,
    val active: Boolean
)

FAQ

How do I convert JSON to Kotlin types?

Paste any JSON sample. The data classes are inferred from the values and nesting, entirely in your browser. Nothing is uploaded.

How are nested objects handled?

Each distinct nested object becomes its own named type, referenced from the parent, arrays of objects included.

What about optional or null fields?

Fields that are null or missing in parts of the sample are typed as optional/nullable in the generated code.

Can I paste multiple samples?

Paste an array of objects: the type is inferred from the union of all items, which catches optional fields a single sample would miss.

Does it work with kotlinx.serialization?

Yes. The generated data classes carry no annotations, so add @Serializable (kotlinx) or Moshi/Jackson annotations to match your stack.

Is my JSON uploaded?

No. Generation runs 100% in your browser via quicktype's engine. Check DevTools: zero network requests.

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