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JSON to Kotlin Data Class Converter

· Last updated：2026-06-20

Convert JSON data into Kotlin data classes with @SerializedName annotations, nullable handling, and nested type inference

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Written by the Elysia Tools team
JSON107

Tool usage guide

Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Category
Development
Input types
textarea, text, checkbox
Output type
text
Sample coverage
4
API ready
Yes

Overview

The JSON to Kotlin Data Class Converter simplifies Android and backend development by instantly generating clean, type-safe Kotlin data classes from raw JSON payloads. It automatically infers nested object structures, handles arrays, generates @SerializedName annotations for serialization libraries, and supports nullable property configurations.

When to use

  • When integrating a new REST API and you need to quickly generate Kotlin Data Transfer Objects (DTOs) from JSON response payloads.
  • When migrating legacy Java models or manual JSON parsing code to clean, idiomatic Kotlin data classes.
  • When configuring serialization models that require custom field mapping annotations alongside nullable property definitions.

How it works

  1. 1Paste your raw JSON payload into the JSON Input text area.
  2. 2Specify the Root Type Name and toggle the Nullable Properties option if your API fields can be null.
  3. 3Copy the generated Kotlin code, complete with nested classes and @SerializedName annotations, directly into your project.

Use cases

  • Generating Retrofit API response models for Android application development.
  • Creating Kotlin DTOs for Spring Boot or Ktor backend services consuming external JSON APIs.
  • Rapidly prototyping data structures during initial API design phases.

Compare alternatives

  • Convert JSON Schema JSON/YAML definitions into ready-to-use Zod schemas with nested objects, arrays, enums, and common validation rules

  • Convert structured service logs into Mermaid or PlantUML sequence diagrams, with optional latency and error annotations

  • Convert JSON data into C# classes with PascalCase properties, JsonPropertyName attributes, and nested type inference

Who it's for

Best for

  • Convert JSON text in the browser.
  • Repeatable jobs with JSON text and the same settings every time.
  • Jobs where the output is plain text.

Not ideal for

  • Fully automated batch jobs — this page is built for interactive use; use the API endpoint for scripts.
  • Content in other formats — this tool expects JSON text.

Edge cases & common failures

  • Trailing commas or single quotes

    Strict JSON parsers reject them — remove trailing commas and switch to double quotes before validating or formatting.

  • Very large files

    Large files take longer and can hit browser memory limits — try a smaller sample first.

  • Skipping the output check

    Compare the first rows or pages of the output with the input before using it in production.

Examples

1. Generating Android API Response Models

Android Developer

Background

An Android developer is integrating a third-party weather API that returns a complex nested JSON structure.

Problem

Manually writing Kotlin data classes for a nested JSON response with dozens of fields is time-consuming and error-prone.

How to use

Paste the weather API JSON response into the input, set the Root Type Name to 'WeatherResponse', check the 'Nullable Properties' option to handle missing fields safely, and generate the code.

Root Type Name: WeatherResponse, Nullable Properties: True

Outcome

Instantly generates a set of Kotlin data classes with @SerializedName annotations and nullable types, ready to be used directly with Retrofit.

2. Creating Backend DTOs for User Profiles

Kotlin Backend Engineer

Background

A backend engineer using Ktor needs to parse incoming user registration payloads containing nested address and role arrays.

Problem

Needs to quickly create non-nullable Kotlin data classes that match the incoming JSON structure exactly.

How to use

FAQ

Does this tool support nested JSON objects?

Yes, it automatically detects nested objects and generates corresponding nested Kotlin data classes.

How does the tool handle JSON arrays?

It infers the item type within the array and represents it as a Kotlin List of that type.

Can I make all generated properties nullable?

Yes, checking the Nullable Properties option will append a question mark to all property types, making them nullable.

What annotations are added to the generated Kotlin classes?

The tool generates @SerializedName annotations for each property to ensure compatibility with serialization libraries like Gson.

Do I need to define names for nested classes manually?

No, the converter automatically infers appropriate class names for nested objects based on their JSON key names.

Hub

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Paste the user registration JSON payload, set the Root Type Name to 'UserRegistration', leave 'Nullable Properties' unchecked for strict non-null validation, and copy the output.

Root Type Name: UserRegistration, Nullable Properties: False

Outcome

Generates clean, non-nullable Kotlin data classes with nested classes for the address and list types for the roles.

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