Javalin OpenAPICompile-time API Documentation

Generate OpenAPI specifications and JSON Schemas at compile time with zero runtime reflection. Annotation-driven, type-safe, and ready for Swagger UI and ReDoc.

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Compile-time Generation

Schemas are generated during compilation using annotation processing. No runtime reflection, no classpath scanning, no startup overhead.

Two Modes

Generate OpenAPI 3.1.0 endpoint documentation with @OpenApi, or standalone JSON Schema 2020-12 files with @JsonSchema — using the same annotation processor.

Swagger UI & ReDoc

Built-in plugins serve Swagger UI and ReDoc out of the box. Register the plugin and your interactive API documentation is live.

Schema Customization

Control property names with @OpenApiNaming, add examples with @OpenApiExample, override types with @OpenApiPropertyType, and validate with constraint annotations.

Enum Support

Rename values with @OpenApiName, apply naming strategies with @OpenApiNaming, create integer enums with @OpenApiPropertyType, and add descriptions.

Compile-time Configuration

Fine-tune the annotation processor with openapi.groovy — custom type mappings, property filters, and embedded type processors.