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JSON to Kotlin Converter

Working with JSON data and need Kotlin models fast? JSON is natively parsed by all major runtimes — no schema required to begin parsing. This free, browser-based converter parses your JSON and generates clean, production-ready Kotlin code — no account required.

Generate Kotlin data classes with null safety, default values, and Moshi/Gson serialization annotations.

How to use this converter

  1. Paste your JSON into the left editor panel
  2. Click Generate
  3. Copy the generated Kotlin code from the right panel

No account. No upload. No tracking. Runs entirely in your browser.

Example Kotlin output

import com.google.gson.annotations.SerializedName
 
data class Address(
    @SerializedName("city") val city: String,
    @SerializedName("zip") val zip: String
)
 
data class User(
    @SerializedName("id") val id: Long,
    @SerializedName("name") val name: String,
    @SerializedName("email") val email: String? = null,
    @SerializedName("address") val address: Address
)

Why automate JSON-to-Kotlin conversion?

Writing Kotlin data class definitions by hand from JSON is:

  • Tedious — especially for deeply nested or large JSON payloads
  • Inconsistent — naming conventions drift when done manually across a team
  • Fragile — when the JSON schema changes, hand-written models lag behind

Kotlin data classes automatically generate equals(), hashCode(), copy(), and toString() — perfect for immutable data transfer objects.

This converter handles all of that automatically, giving you idiomatic Kotlin code that matches your JSON structure exactly.

Kotlin and JSON: what you need to know

Kotlin is a concise, null-safe JVM language language, official Android language and popular for Spring Boot on JVM. It uses data class based with null-safety built in for structured data — making it a natural fit for JSON-driven applications.

What the converter generates

Output uses Kotlin data class syntax with nullable types (String?) for optional fields. Constructor parameters include @SerializedName or @Json annotations for Gson and Moshi compatibility.

A common gotcha

Kotlin distinguishes between nullable (String?) and non-nullable (String) types — this converter infers nullability from your input data.

JSON input characteristics

JSON supports nested objects, arrays, strings, numbers, booleans, and null. Tools like jq, Postman, and browser DevTools make JSON the most developer-friendly data exchange format.

When should I use this converter?

Use this for Android or Kotlin Multiplatform projects where you need idiomatic data classes from API response payloads without manually mapping each field.

Common use cases

  • Generating data classes for Retrofit + Gson/Moshi in Android projects
  • Creating Kotlin models for Ktor server-side API response handling
  • Producing serializable models for Kotlin Multiplatform shared modules
  • Generating Kotlin models from Android development API responses
  • Creating typed DTOs for Ktor APIs
  • Rapid prototyping with real JSON payloads
  • Keeping Kotlin structs in sync when JSON schemas evolve
  • Onboarding new team members by auto-generating the data layer
  • Validating JSON contract compatibility with Kotlin type definitions

Frequently asked questions

Does this converter support JavaScript Object Notation namespaces and nested structures?

Yes. JSON is natively parsed by all major runtimes — no schema required to begin parsing. The parser handles deeply nested structures and generates matching nested Kotlin data class definitions.

How are optional fields handled in the Kotlin output?

Fields that may be absent or null in your JSON are marked as optional in the generated Kotlin code. Note: Kotlin distinguishes between nullable (String?) and non-nullable (String) types — this converter infers nullability from your input data.

Can I use the output directly in a Android development project?

Yes. The generated Kotlin code follows idiomatic patterns for Android development — you can copy it directly into your project.

Does this work for large JSON payloads?

Yes. The converter is optimized for large and deeply nested JSON structures, running entirely in the browser without page reloads or server round-trips.

Related tools on LangStop

If you work frequently with JSON and Kotlin, bookmark this page to skip the manual model-writing step entirely.