JSON to Kotlin Data Class Converter

How JSON maps to Kotlin types

The tool reads the top-level keys of a JSON object and writes one constructor parameter per key. Types come from the sample values you paste:

• number becomes Double, boolean becomes Boolean and string becomes String.
• null, arrays and nested objects become Any.
• Every parameter is a nullable val, for example val id: Double?.

JSON to Kotlin example

Input:

{"id":1,"name":"Ada","active":true,"address":{"city":"London"},"tags":["math"]}

// Kotlin output
data class Root(
    val id: Double?
    val name: String?
    val active: Boolean?
    val address: Any?
    val tags: Any?
)

What to review before you use the Kotlin output

• Paste a JSON object, not a bare array. The tool walks the top-level keys, so an array root produces meaningless index names.
• Nested objects and arrays are not expanded into their own types. In the example, address and tags both fall back to a generic type, so write those types by hand.
• One sample cannot show which fields are optional or which numbers are integers. Numbers are always mapped to a floating-point type.
• The tool writes one parameter per line without commas between them. Add a comma after each parameter except the last before you compile.
• Remove the ? from parameters that are always present, and add a serialization annotation if your library needs one.

Related: JSON to Java, JSON to C#, JSON to TypeScript, JSON Formatter