JSON to Kotlin Data Class Converter
Convert JSON objects to Kotlin data classes with automatic type inference, nullable handling, and serialization annotations. Supports kotlinx.serialization, Gson, Moshi, and Jackson. Perfect for Android development, backend APIs, and Kotlin Multiplatform projects.
Conversion Options
Recommended Settings
Kotlin Data Class Best Practices
- •Use 'val' for immutable properties - data classes work best with immutability
- •Only make fields nullable (Type?) when they can actually be null in your API
- •Choose kotlinx.serialization for multiplatform projects, Gson for Android-only apps
- •Enable snake_case to camelCase conversion for Kotlin naming conventions
- •Sort fields alphabetically for better code organization and consistency
Serialization Library Comparison
- •kotlinx.serialization: Official, compile-time safe, supports Kotlin Multiplatform
- •Gson: Popular for Android, uses reflection, simple to use but slower
- •Moshi: Modern, efficient, supports both reflection and codegen modes
- •Jackson: Feature-rich, enterprise-grade, supports XML/YAML beyond JSON
- •Plain Kotlin: No dependencies, manual parsing required, full control
Pro Tips
- •Paste JSON and it auto-validates - conversion happens automatically when valid
- •Nested objects are converted to separate data classes automatically
- •Arrays are converted to List<T> with type inference from first element
- •All processing happens in your browser - your data never leaves your device
Most Popular
Most users choose val + kotlinx.serialization + camelCase conversion for modern Kotlin projects
When to Use This Tool
Convert JSON API responses to Kotlin data classes for your Android app. Use with Retrofit, Room, or Jetpack Compose. Choose Gson for simple Android-only apps or kotlinx.serialization for modern multiplatform projects. Data classes provide automatic equals(), hashCode(), and toString() implementations perfect for Android development.
Generate Kotlin data classes for server-side applications using Ktor, Spring Boot, or Micronaut. Convert JSON API contracts into type-safe Kotlin models. Use Jackson for Spring Boot compatibility or kotlinx.serialization for Ktor. Data classes ensure compile-time safety and reduce boilerplate in backend code.
Create shared data models for Kotlin Multiplatform Mobile (KMM) or Kotlin Multiplatform (KMP) projects. Use kotlinx.serialization for cross-platform JSON parsing that works on Android, iOS, JVM, and JavaScript. Data classes enable code sharing between platforms while maintaining type safety.
Build type-safe API client libraries by converting API documentation JSON examples to Kotlin data classes. Use Moshi with code generation for efficient networking. Data classes with serialization annotations ensure accurate JSON mapping and provide autocomplete support in IDEs for API consumers.
How It Works
Paste your JSON data into the input field on the left side
The tool automatically validates JSON syntax to ensure it's properly formatted
Select property modifier: val (immutable, recommended) or var (mutable)
Choose nullable strategy: only null values or make all fields nullable
Pick serialization library: kotlinx, Gson, Moshi, Jackson, or none
Configure additional options: defaults, sorting, naming conversion, package declaration
Click 'Convert to Kotlin' or paste valid JSON to trigger automatic conversion
The tool detects Kotlin types: Int, Long, Double, Boolean, String, List<T>, nested classes
Nested objects are converted to separate data classes automatically
Copy the Kotlin code to clipboard or download it as a .kt file
All processing happens in your browser - your JSON data never leaves your device
100% Private
Files never leave your device. All processing happens locally in your browser.
Lightning Fast
Powered by Pure JavaScript for optimal performance on modern browsers.
Secure
No data collection, no tracking, no sign-up required.
Frequently Asked Questions
What is a Kotlin data class?
A data class in Kotlin is a special class designed to hold data. The 'data' keyword automatically generates useful methods like equals(), hashCode(), toString(), copy(), and component functions for destructuring. Data classes are perfect for modeling JSON responses because they're concise and provide value equality by default.
Should I use 'val' or 'var' for properties?
Use 'val' (immutable) for data classes in most cases. Immutability makes your code safer, easier to reason about, and thread-safe. Data classes work best with immutable properties. Only use 'var' (mutable) if you specifically need to modify properties after object creation, which is rare for JSON models.
When should I make fields nullable (Type?)?
Make fields nullable only when they can actually be null in your JSON API. If a field is always present with a value, use non-nullable types (Int, String). If a field might be null or missing, use nullable types (Int?, String?). The 'Only null values' option is recommended - it makes fields nullable only when they're null in your sample JSON.
Which serialization library should I choose?
Choose based on your project: kotlinx.serialization for Kotlin Multiplatform and modern projects (compile-time safe, official), Gson for Android-only apps (simple, popular), Moshi for modern Android (efficient, Square), Jackson for Spring Boot backend (feature-rich, enterprise), or None for manual parsing with full control.
What's the difference between Int, Long, and Double?
Int stores 32-bit integers (-2,147,483,648 to 2,147,483,647). Long stores 64-bit integers for larger numbers. Double stores decimal numbers. The tool automatically chooses: Int for small whole numbers, Long for large whole numbers, and Double for decimals. This matches Kotlin's type system and prevents overflow errors.
How does snake_case to camelCase conversion work?
When enabled, the tool converts JSON field names from snake_case (user_name, is_active) to Kotlin's camelCase convention (userName, isActive). Serialization annotations (@SerialName, @SerializedName) preserve the original JSON field names for correct parsing. This follows Kotlin naming conventions while maintaining API compatibility.
What happens with nested objects and arrays?
Nested objects are automatically converted to separate data classes with PascalCase names derived from the field name. Arrays become List<T> with type inference from the first element. Empty arrays default to List<Any>. All nested classes are generated before the main class for proper compilation order.
Is my JSON data secure using this tool?
Your data is completely private. All conversion happens entirely in your browser using JavaScript - nothing is sent to any server. The tool works offline after initial load. However, remember that the generated Kotlin code contains your data structure - review it before sharing or committing to version control.