#2121st of 45 in Backend and cloud templates
javalin
Lightweight web framework for Java and Kotlin with WebSockets and HTTP/2
Documentation ↗
(opens in a new tab)Website ↗
(opens in a new tab)Repository on GitHub ↗
(opens in a new tab)
- Stars
- 8.4k
- License
- Apache-2.0
- Last commit
- Oct 2026
- Last release
- Oct 2026
- Language
- Kotlin
8,199 on 21 Apr 20268,379 on 10 Nov 2026
From GitHub's daily star counts.
Checked on GitHub.
Overview
Javalin is a web library for Java and Kotlin that handles HTTP routing, WebSockets, HTTP/2, async requests, static files, JSON mapping and file uploads. It avoids annotations, reflection and base classes to extend, so handlers are plain lambdas registered on a config object. It has no AI features; it fits this list only as a generic backend service base, with plugins for OpenAPI and SSL.
Who it is for: Java and Kotlin developers building HTTP or WebSocket backend services
Strengths
- No annotations, reflection or required base classes; handlers are plain lambdas
- Same API in Java and Kotlin, with examples for both
- Built-in WebSockets, static files, JSON mapping and file uploads
- Plugin system, including OpenAPI 3.0 generation and SSL (PEM, PKCS12, JKS)
Weaknesses
- No AI, model or agent integration; only a generic HTTP backend
- Not a template: no auth, database or billing wired in
- OpenAPI support is a separate plugin that relies on annotations
- Dependency, JSON mapper and database choices are left to you
What it needs
- Kotlin
- Needs JVM (Java or Kotlin), Maven or Gradle
Quick answers
Is javalin open source?
Yes. Its code is on GitHub under the Apache-2.0 license.
Also in Backend and cloud templates
See all 45| Rank | Project | Score |
|---|---|---|
| 1 | fastapiPython web framework for typed REST APIs with automatic OpenAPI docs | 90 out of 100 |
| 2 | fiberExpress-style HTTP web framework for Go, built on fasthttp | 90 out of 100 |
| 3 | generator-jhipsterCode generator for Java apps with Angular, React or Vue frontends | 90 out of 100 |
| #4 | serverlessCLI that deploys AWS Lambda code and infrastructure from serverless.yml | 88 out of 100 |
| #5 | echoMinimalist Go web framework with a radix-tree router and middleware | 86 out of 100 |