# javalin/javalin

A simple and modern Java and Kotlin web framework

Repository: https://github.com/javalin/javalin
Canonical: https://ross.abutalabs.com/products/javalin
Homepage: https://javalin.io
Language: Kotlin
License: Apache-2.0
License Family: permissive
Topics: kotlin, java, rest-api, web-framework, microservice, servlet, jetty, javalin, hacktoberfest
Last push: 2026-08-15T16:29:24+00:00

## Health v2 (maintenance only)
Score: 98/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 97, release rhythm 97, longevity 100
- inputs: {"age_days": 3440, "days_push": 18, "days_rel": 20, "gap_med": 20.5, "n_releases_24m": 17}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 8340, forks 647 (observed 2026-08-28T04:10:20.391348+00:00)

## What it is
Javalin is a lightweight, simple web framework for Java and Kotlin built on top of Jetty, supporting REST APIs, WebSockets, static file serving, and OpenAPI. It offers a fluent API designed for interoperability between Java and Kotlin with very few concepts to learn.

## Use cases
- build a REST API in Java or Kotlin
- create a lightweight microservice on the JVM
- serve an SPA backend with static files from one server
- add websocket endpoints to a JVM application
- generate OpenAPI documentation with Swagger UI for a Java API
- replace Spring Boot with a simpler web framework
- run a small HTTP server with virtual threads support

## When to choose
- you want a minimal, easy-to-learn REST API framework on the JVM
- you need Java and Kotlin interoperability with one consistent API
- you want Jetty-level performance with full Jetty configurability including SSL and HTTP3
- you prefer a Sinatra/Koa-style micro framework over heavyweight MVC frameworks

## When to avoid
- you need a full MVC framework with built-in ORM, dependency injection, and batteries included
- your team is heavily invested in Spring ecosystem conventions
- you need reactive/non-blocking programming as the primary model

## Facets
- artifact type: framework
- maturity: active
- function: web-framework, http-server, routing, websocket, middleware, api-framework
- domain: web-development, backend, apis, microservices
- platform: jvm, cross-platform
- tags: rest-api, jetty, openapi, micro-framework, sinatra-inspired, servlet

## Member repositories
- javalin/javalin (main) score 98

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:10:20.391348+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-29T17:27:43.237630+00:00, confidence not recorded.
  - readme: https://github.com/javalin/javalin (fetched 2026-08-28T04:10:20.391348+00:00, sha b55a6e766b08)
  - homepage: https://javalin.io (fetched 2026-08-29T08:27:34.133695+00:00, sha 9b01e3b4c44b)
  - site_page: https://javalin.io/documentation (fetched 2026-08-29T08:27:34.143640+00:00, sha 3a98fb023d9a)
  - site_page: https://javalin.io/about (fetched 2026-08-29T08:27:34.147805+00:00, sha 024dbac91b2b)
- Data as of 2026-08-30T08:39:29.467469+00:00.