kotlinx-schema-json

Type-safe JSON Schema models and DSL compliant with JSON Schema Draft 2020-12.

Provides Kotlin models for programmatic JSON Schema construction with full kotlinx-serialization support.

Platform Support: Multiplatform (Common, JVM, JS, Native, Wasm) • Kotlin 2.2+ • Requires kotlinx-serialization-json

Key Classes

• JsonSchema - root schema model with type-safe property definitions

• FunctionCallingSchema - OpenAI/Anthropic function calling format

• DSL builders - fluent API for schema construction

Example

val schema = jsonSchema {
    name = "User"
    schema {
        property("id") {
            required = true
            string { format = "uuid" }
        }
        property("role") {
            oneOf {
                discriminator(propertyName = "type") {
                    "admin" mappedTo "#/definitions/AdminRole"
                }
            }
        }
    }
}

Features

• Type-safe property definitions (string, number, integer, boolean, array, object)

• Polymorphism support (oneOf, anyOf, allOf with discriminators)

• Type-safe enums using native Kotlin collections

• Full kotlinx-serialization integration

Related Specifications

• JSON Schema Draft 2020-12

• OpenAI Function Calling

• Anthropic Structured Outputs