JSON to Kotlin Data Class Generator

Android and Kotlin backends usually parse JSON into data classes. Paste a sample response and get Kotlin data classes ready for kotlinx.serialization, Gson or Moshi: nested objects become their own classes, arrays become List<T>, values that are null or missing in some samples become nullable, and snake_case keys become camelCase properties with the original key kept in @SerialName, @SerializedName or @Json. Numbers beyond the Int range become Long.

How to use this tool

1. Paste a representative JSON sample — arrays with several items give the best types.
2. Enter the root class name and, optionally, a package.
3. Pick kotlinx.serialization, Gson, Moshi or no annotations.
4. Choose val or var, when properties are nullable, and whether to add default values.
5. Copy the code into a .kt file.

Formula

whole number → Int (Long beyond ±2,147,483,647) · fraction → Double · true/false → Boolean · text → String · [ … ] → List<T> · { … } → data class

Values at the same place in different samples are merged: Int and Double become Double, mixed kinds become JsonElement (kotlinx) or Any. A property that is null in some sample or missing from some array item is nullable. Identical shapes share one class; list item classes are named from the singular of the key (orders → Order). Hard keywords such as in or object are written in backticks.

Example

The sample user gives three classes. User has id: Int, name: String, isActive: Boolean (annotated @SerialName("is_active")), balance: Double, followers: Long (3,000,000,000 is over Int.MAX_VALUE), tags: List<String>, address: Address, orders: List<Order> and manager: JsonElement? = null. Order has orderId: String, total: Double, items: Int and coupon: String? = null, because only the second order has a coupon.