Convert JSON to Kotlin online, free. JSON is the dominant data-interchange format for web APIs and config. Kotlin data classes model structured data with null-safety. JSON to Kotlin conversion parses your JSON against the ECMA-404 / RFC 8259 grammar (https://www.rfc-editor.org/rfc/rfc8259), builds an in-memory model of its keys, nested objects and arrays, then emits ready-to-use Kotlin types as data classes with nullable types following the Kotlin docs conventions. Processing runs in your browser in JavaScript with no upload or server round-trip — no size limit beyond your device's memory, so multi-megabyte documents convert in milliseconds and sensitive payloads never leave your machine. Typical uses include Android apps, Ktor services and kotlinx.serialization.
It maps the full structure of your JSON onto idiomatic Kotlin types, following the Kotlin docs conventions. 100% free, no registration, and complete privacy — everything runs locally in your browser, so your data never touches a server.
Paste JSON and generate Kotlin types from Kotlin immediately. Conversion runs client-side, so there is no upload wait and large documents stay fast.
Nested JSON objects, tables and arrays are mapped faithfully onto Kotlin, including nested types and optional fields.
Your JSON never leaves your device — everything is processed locally in JavaScript, with nothing logged or stored.
Unlimited conversions with no account, no quotas, and no watermark. Works on desktop and mobile.
A JSON document and its Kotlin equivalent:
JSON input:
{
"title": "Dune",
"pages": 412,
"available": true
}Output:
@Serializable
data class Book(
val title: String,
val pages: Int,
val available: Boolean,
)Paste your JSON into the editor and press "Convert to Kotlin". The tool parses it against the ECMA-404 / RFC 8259 grammar, then generates Kotlin types following Kotlin docs conventions — instantly and entirely in your browser. You can validate or format the JSON first to be sure it is clean.
JSON already uses objects, arrays and typed scalars, so mapping to Kotlin is close to one-to-one: objects become types or structs, arrays become lists, and numbers, booleans and null keep their types.
Optional or nullable members in the generated Kotlin are inferred from keys missing in some records of your JSON, following Kotlin docs. Include the optional fields in your sample so they are typed correctly.
JSON (JavaScript Object Notation) (JSON) — JSON is the dominant data-interchange format for web APIs and config. Kotlin data classes (Kotlin) — Kotlin data classes model structured data with null-safety. This converter maps the structure of your JSON onto Kotlin so you can use it for Android apps.
Yes. Invalid JSON is flagged with a clear error before anything is converted. Common JSON problems to check are matched braces and brackets, double-quoted keys, and no trailing commas. Starting from clean input keeps the generated Kotlin accurate.
Yes. The entire JSON-to-Kotlin conversion runs locally in your browser in JavaScript — your JSON is never uploaded, logged or stored. That matters when the data is something like REST/GraphQL API payloads, which should not leave your machine.
The generated Kotlin is ready for Android apps, Ktor services and kotlinx.serialization. Copy or download it and drop it straight into your codebase.
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