Javalin, a Java/Kotlin REST API Framework

In plain words

Javalin is a lightweight web framework for building REST APIs in Java and Kotlin. It is designed for developers who want to create web applications without learning complex concepts or extending classes. The framework emphasizes simplicity with a minimal codebase and straightforward syntax for defining routes and handling requests.

written from the facts on this page · September 2026

From the sources

Unlike other Java and Kotlin web frameworks, Javalin has very few concepts that you need to learn. You never extend classes and you rarely implement interfaces. Javalin is just a few thousand lines of code on top of Jetty, and its performance is equivalent to raw Jetty code. Due to its size, it's very easy to reason about the source code. Other Java and Kotlin web frameworks usually offer one version for each language. Javalin is being made with inter-operability in mind, apps are built the same way in both Java and Kotlin. Javalin is designed to be simple and blocking, as this is the easiest programming model to reason about. But, if you set a Future as a result, Javalin switches into…from javalin.io

• 
  Javalin 1.0 – A Kotlin/Java web framework2017 · javalin.io · ▲271
• 
  I finished v5 of a JVM framework I've spent spent half a decade making2022 · javalin.io · ▲377

  ForewordJavalin is a Java and Kotlin web framework which focuses on simplicity and Java/Kotlin interoperability.It supports WebSockets and HTTP3, and it uses...

• 
  My Kotlin/Java REST Library Javalin Reaches v0.4.0 (CORS, Uploads, ++)2017 · javalin.io · ▲11

  CORSJavalin 0.4.0 adds built-in CORS support with app.enableCorsForOrigin(

• 
  Javalin REST Library – Rewritten in Kotlin2017 · javalin.io · ▲5

  Javalin release notes, announcements, and changelog.

• 
  1 KB JavaScript library for building front end apps2017 · github.com · ▲242

  1kB-ish JavaScript framework for building hypertext applications - hyperapp/hyperapp

• 
  Restate – Low-latency durable workflows for JavaScript/Java, in Rust2024 · restate.dev · ▲185

  We'd love to share our work with you: Restate, a system for workflows-as-code (durable execution). With SDKs in JS/Java/Kotlin and a lightweight runtime built in Rust/Tokio. https://github.com/restatedev/ https://restate.dev/ It is free and open, SDKs are MIT-licensed, runtime permissive BSL (basically just the minimal Amazon defense). We worked on that for a bit over a year. A few points I think are worth mentioning: - Restate's runtime is a single binary, self-contained, no dependencies aside from a durable disk. It contains basically a…

• 
  /dev/null▲468

  a social network for devs

  Dev tools · 2d ago · dev-null.sh

• 
  Whiteboard (YC W26) – an open-source IDE for thoughtful software design▲423

  open-source IDE for thoughtful software design. Contribute to devdotfast/whiteboard development by creating an account on GitHub.

  Dev tools · 27d ago · github.com

• 
  Reladraw – A diagram language where you decide where to place things▲411

  Contribute to reladraw/reladraw development by creating an account on GitHub.

  Dev tools · 25d ago · github.com

• 
  OpenBot▲362

  Grok Bot alternative: free, local, open-source, multiplayer

  Dev tools · 22d ago · openbot.run

• 
  Talanoa▲340

  Hi HN, I’m a fullstack developer, and honestly, I’ve lost count of how many side projects I’ve worked on over the years. But one idea kept coming back to me: a different kind of email client. It first came to me in 2014: “What if we could handle emails more like conversations?” Every year, I’d revisit this concept in my “Build Notes.” Ten years later, no one had built exactly what I had in mind — so I finally decided to do it myself. That’s how Talanoa was born. I wanted something focused on people, not timelines. I was tired of marking messages as unread just to remember to reply later, or…

  Dev tools · 20d ago · talanoa.email

• 
  CoreSpeed▲332

  One MCP for everything your agents need: apps, memory, tools

  Dev tools · 27d ago · corespeed.io

• 
  Framer Design▲1,008

  Design, code and collaborate. Now all-in-one.

  Dev tools · 2017 · framer.com

• 
  Not Hotdog▲907

  An app that shows if your food is a hotdog 🌭

  Life & fun · 2017

• 
  Ludus Beta▲906

  A limitless presentation tool for designers.

  Work · 2017 · ludus.one

• 
  Startup Graveyard▲877

  History shouldn't have to repeat itself

  Life & fun · 2017 · startupgraveyard.io

• 
  Good Sales Emails▲813

  Best sales emails from great companies

  Growth · 2017 · goodsalesemails.com

• 
  Things 3.0▲757

  Complete revamp of the original, award-winning task manager

  Work · 2017 · culturedcode.com