● KOTLIN DATA CLASSES · 100% BROWSER-BASED

JSON to Kotlin

Paste a JSON sample and get Kotlin data classes, instantly and entirely in your browser. Optional fields, nullability and nested types are inferred from the sample — and anything the sample cannot settle is reported rather than guessed.

Target Root name

JSON sample

TypeScript interface

Type definitions will appear here

What it generates

Kotlin data classes from a sample

Generates @Serializable data class declarations with @SerialName where the Kotlin name differs from the JSON key.

Optional and nullable fields are typed T? with a = null default — null safety is the point of the language, so it is not glossed over.

Limits

What a sample cannot tell you

Types are inferred from one sample. A field absent from your sample will be absent from the output, and a field that happens to hold only whole numbers will be typed as an integer even if it can hold decimals. Paste the widest sample you have. For a guarantee rather than an inference, start from a JSON Schema.

Worked example

What Kotlin output looks like

Generated from two sample records, one of which has an extra field and a null. This is the actual output, not an illustration:

@file:Suppress("unused")

import kotlinx.serialization.SerialName
import kotlinx.serialization.Serializable

@Serializable
data class Root(
    val id: Long,
    val userName: String,
    val isActive: Boolean,
    val score: Double,
    val tags: List<String>,
    val address: Address,
    val lastSeen: String,
    val nickname: String? = null
)

@Serializable
data class Address(
    val city: String,
    val postcode: Any? = null
)

Kotlin specifics

The three things that differ by language

Large integers

Kotlin has Long, so a 64-bit identifier survives — unlike the JavaScript, Go v1 and TypeScript targets. Values beyond 2⁵³−1 are typed Long rather than Int.

Optional against nullable

Optional and nullable fields are typed T? with a = null default. Null safety is the point of the language, so this is not glossed over: a field that was missing from one sample is not declared non-null.

Names that are not identifiers

@SerialName is emitted whenever the Kotlin property name differs from the JSON key, so camelCase conventions do not break deserialisation.

Other targets