kt-schema-apt

Compile-time JSON Schema generation for plain Java projects via a JSR 269 (javax.annotation.processing) annotation processor.

Analyzes @Schema-annotated Java types — or every type under a configured root package — at compile time, writing one JSON Schema resource per type. No Kotlin required in consuming code.

Platform Support: JVM only • Build-time only • Java 17+

Generated Output

@Schema
public record User(String name) {}

// Generated resource:
// META-INF/kt-schema/schemas/com/example/User.json

Unlike kt-schema-ksp, this module has no Kotlin code to attach extension properties to, so it writes the serialized JsonSchema directly as a classpath resource instead of generating Kotlin source.

Configuration

Processor options, set via javac -A compiler arguments:

• me.kpavlov.kt.schema.rootPackage — process every top-level type under this package (and sub-packages), in addition to @Schema-annotated types

See Java Annotation Processor Guide.

Features

• Reuses the same TypeGraphToJsonSchemaTransformer as kt-schema-ksp, so output (

  $id/$

  defs/$ref/nullability) is identical

• Recognizes description/ignore/name-override annotations from Jackson, LangChain4j, Koog, etc. via the shared Introspections config, same as KSP and reflection