Javalin Swagger UI

The SwaggerPlugin serves Swagger UI for interactive API exploration. Register it alongside the OpenApiPlugin to get a browser-based endpoint explorer at /swagger:

config.registerPlugin(SwaggerPlugin())

Configuration

Pass a lambda to customize the plugin. The most common options are the documentation source path and the UI route:

config.registerPlugin(SwaggerPlugin { swagger ->
    swagger.documentationPath = "/openapi"  // where the OpenAPI JSON is served
    swagger.uiPath = "/swagger"             // where Swagger UI is mounted
    swagger.title = "My API Documentation"  // HTML page title
})

All available options:

Property	Default	Description
documentationPath	/openapi	Path to the OpenAPI JSON endpoint
uiPath	/swagger	Route where Swagger UI is served
title	"OpenApi documentation"	HTML page title
version	"5.31.2"	Swagger UI bundle version
basePath	""	Base path prefix for reverse proxy setups
roles	[]	Access control roles
validatorUrl	"https://validator.swagger.io/validator"	Validator endpoint URL
tagsSorter	"'alpha'"	Tag sorting strategy
operationsSorter	"'alpha'"	Operation sorting strategy
webJarPath	/webjars/swagger-ui	WebJar serving location

Version Switching

If your API serves multiple specification versions, you can populate the Swagger UI version dropdown:

swagger.injectCustomVersion("v1", "/openapi?v=v1")
swagger.injectCustomVersion("v2", "/openapi?v=v2")

Customization

You can inject custom stylesheets and scripts to theme or extend the UI:

swagger.injectStylesheet("/custom/swagger-theme.css")
swagger.injectJavaScript("/custom/swagger-init.js")

When running behind a reverse proxy that adds a base path, set basePath so the UI loads assets correctly:

swagger.basePath = "/api"

SwaggerPlugin is repeatable — you can register multiple instances for different API versions or configurations.