JSON to Kotlin Data Class Converter

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Generate Kotlin Data Classes from JSON Automatically

Kotlin has become the go-to language for Android development and is rapidly gaining ground in backend development with frameworks like Ktor and Spring Boot. When your Kotlin application needs to consume JSON data - from REST APIs, configuration files, or WebSocket messages - you need data classes that match the JSON structure. The JSON to Kotlin Data Class Converter generates those classes automatically from sample JSON, complete with proper type annotations and serialization support.

Writing Kotlin data classes by hand for a complex API response is not just slow - it is error-prone. A nested JSON object with thirty fields, some nullable, some containing arrays of other objects, can easily produce ten or more data classes. Getting every type, every nullability annotation, and every property name correct takes careful attention. This converter does it instantly and accurately.

How the Conversion Works

Paste any valid JSON into the tool and the JSON to Kotlin Data Class Converter analyzes the structure recursively. Each JSON object becomes a Kotlin data class. String values produce String properties. Numbers become Int, Long, or Double depending on the value. Booleans become Boolean. Null values produce nullable types with the ? suffix. Arrays produce List<T> properties with the element type inferred from the array contents.

Nested JSON objects generate their own named data classes, and the parent class references them by type. The naming convention follows Kotlin standards - PascalCase for class names, camelCase for properties. JSON keys that use snake_case or other conventions are preserved in @SerializedName annotations (for Gson) or @Json(name = ...) annotations (for Moshi), while the Kotlin property uses idiomatic camelCase.

Serialization Library Support

Different projects use different JSON serialization libraries. Android projects commonly use Gson or Moshi. Kotlin Multiplatform projects use kotlinx.serialization. Spring Boot projects might use Jackson. The JSON to Kotlin Data Class Converter produces annotations for your chosen library, so the generated classes integrate seamlessly with your existing serialization setup.

For kotlinx.serialization, the output includes @Serializable class annotations and @SerialName property annotations. For Gson, it uses @SerializedName. For Moshi, it generates @Json(name = ...). For Jackson, it produces @JsonProperty. Switching between libraries is a single option change - the structural class definitions remain the same.

Nullable Safety That Matches Kotlin Philosophy

One of Kotlin's greatest strengths is its null safety system, and this converter respects it. Fields that are null in the sample JSON produce nullable types (String?, Int?). Fields that are present with values produce non-nullable types. This distinction matters because Kotlin's compiler enforces null checks at compile time - a non-nullable property that receives a null value at runtime will throw an exception, which is exactly the safety net you want.

For fields where nullability is ambiguous from a single sample, the converter defaults to nullable types - the safer choice. You can always tighten the type to non-nullable if you know the field is always present. It is much easier to remove a question mark than to debug a NullPointerException in production.

Android Development Workflow

For Android developers, this tool fits directly into the API integration workflow. Make a network request with Retrofit, capture the JSON response from the API documentation or a debugging session, paste it into the JSON to Kotlin Data Class Converter, and get data classes ready for use with your Retrofit interface definitions. The entire round-trip from API exploration to typed Kotlin code takes minutes instead of hours.

The generated classes work immediately with Retrofit's converter factories - add the Gson or Moshi converter, define your API interface with the generated classes as return types, and Retrofit handles the deserialization automatically. Type-safe API consumption with minimal manual effort.

Private, Fast, and Always Ready

The JSON to Kotlin Data Class Converter processes everything in your browser. Your JSON data - which may contain real API responses with user data or business information - stays on your device throughout. No server processes your data, no account is needed, and there are no usage limits. Generate data classes for every endpoint in your API during a single session if you need to. Your data remains yours, and the conversion is always instant.