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JSON to Kotlin

Generate Kotlin classes/structs automatically from a JSON object.

100% Client-Side Local Execution
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What is JSON to Kotlin?

This free online tool turns a sample JSON payload into a ready-to-use data class for Kotlin, so you can use this json to kotlin data class tool to go straight from raw JSON to a typed data class without writing the boilerplate yourself. It is built around Kotlin's actual idiom — a Kotlin data class — rather than a generic one-size-fits-all class, and pairs naturally with kotlinx.serialization or Moshi/Gson for real-world (de)serialization. Use it for json to kotlin data class online or any time you need kotlin data class from json, whether you're scaffolding a new Kotlin project or mapping an existing API response.

Technical Execution

Paste or upload a sample JSON object or array and the tool walks its structure field by field, inferring a concrete Kotlin type for each value — mapping basic JSON types to `String`, `Int`/`Double`, and `Boolean` as appropriate. For nested data, it generates a separate `data class` for every nested JSON object, and types arrays as `List<T>` of the matching element type. On the naming side, it converts snake_case keys to Kotlin's camelCase property convention and adds a `@SerialName("original_key")` (or `@Json(name = ...)`) annotation so the mapping round-trips through serialization. For optional data, fields observed as `null`, or missing from some sample objects, are typed as nullable (`String?`, `Int?`) with sensible defaults where appropriate, matching how Kotlin's null-safety requires every nullable field to be declared explicitly.

Zero Data Storage Guarantee

Everything runs client-side in your browser: the sample JSON you paste in — which may contain real field names, endpoint shapes, or structure from a private API or project — is parsed and converted entirely on your device and is never uploaded to any server. Nothing you enter is logged, stored, or transmitted anywhere, so you can safely paste a real payload from an internal or unreleased API to generate an accurate Kotlin data class. Closing or refreshing the tab clears everything, since no copy of your data ever left your machine in the first place.

How to Use JSON to Kotlin (Step-by-Step Guide)

  1. Copy a representative sample of your JSON (the more fields and nested objects it includes, the more complete the generated data class will be).
  2. Paste it into the input panel of the JSON to Kotlin tool, or click "Upload" to load it from a json file.
  3. Review the auto-detected root name, and rename it if you want the generated Kotlin data class to use a specific class or type name instead of the default.
  4. Click "Generate" to produce the Kotlin data class, which appears instantly in the output panel with syntax highlighting.
  5. Click "Copy" to copy the generated code to your clipboard, or "Download" to save it as a `.kt` file.
  6. Paste the result into your Kotlin project and adjust field names or types if your data has edge cases the sample didn't cover.

Frequently Asked Questions (FAQ)

Q: How does this tool handle nested objects and arrays when converting JSON to Kotlin?
A: The tool generates a separate `data class` for every nested JSON object, and types arrays as `List<T>` of the matching element type That keeps the generated code organized the way a Kotlin developer would structure it by hand, instead of flattening everything into one giant data class.
Q: What happens to fields that are nullable or missing from some records?
A: For optional data, fields observed as `null`, or missing from some sample objects, are typed as nullable (`String?`, `Int?`) with sensible defaults where appropriate, matching how Kotlin's null-safety requires every nullable field to be declared explicitly. If your sample only has one example object, fields that could be null in other records might not be detected as optional — paste a few varied samples (or an array of objects) for the most accurate result.
Q: Is this better than writing the data class by hand?
A: For anything beyond a trivial, flat payload, yes — writing a Kotlin data class by hand for a nested API response means getting every `@SerialName` annotation and nullable type right, and that's tedious to redo whenever the backend response shape changes. The generator produces the same result in seconds and gives you a correct starting point to refine, rather than a blank page.
Q: Is my JSON data safe to paste into this tool, especially if it's from a private API?
A: Yes. Everything runs client-side in your browser: the sample JSON you paste in — which may contain real field names, endpoint shapes, or structure from a private API or project — is parsed and converted entirely on your device and is never uploaded to any server. Nothing you enter is logged, stored, or transmitted anywhere, so you can safely paste a real payload from an internal or unreleased API to generate an accurate Kotlin data class. Closing or refreshing the tab clears everything, since no copy of your data ever left your machine in the first place.
Q: Can I use this as a convert json to kotlin class free?
A: Yes — the tool is commonly used as a convert json to kotlin class free, and works the same way whether you're converting a one-off response for a prototype or generating model code for a production project.
Q: Does the tool rename fields to match Kotlin naming conventions?
A: Yes. It converts snake_case keys to Kotlin's camelCase property convention and adds a `@SerialName("original_key")` (or `@Json(name = ...)`) annotation so the mapping round-trips through serialization, so the generated code reads naturally in Kotlin while still deserializing the original JSON correctly.
Q: What Kotlin library does the generated code work with?
A: The output is written to pair cleanly with kotlinx.serialization or Moshi/Gson, the most common choice for Kotlin developers handling JSON, so you can drop it into an existing project without changing your serialization setup.
Q: Does this tool work for deeply nested or large JSON samples?
A: Yes. The tool recurses through every level of nesting it finds and generates a complete set of linked data class definitions, not just the top level — though for very large samples, trimming it down to one representative record per array is usually enough to get an accurate result.
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