Open q3js.com, pick a server or hit Quick Play, and you are in a live Quake III Arena match with nothing to install. The engine is ioquake3 compiled to WebAssembly, so it is rebuilt from open source rather than decompiled. The hosted site uses officially released demo data.
The original game
Quake III Arena dropped the story campaign of earlier Quake games. Elite warriors fight in arenas for the entertainment of an alien race, the Vadrigar, and single-player is a series of matches against bots. The game was built for multiplayer, and its Dreamcast version holds 93/100 on Metacritic. A public test, Q3Test, launched on April 24, 1999.
Designed by Graeme Devine, Tim Willits and Jennell Jaquays. Programmed by John Carmack, Robert A. Duffy and Jim Dosé. Built on id Tech 3, whose source id released under the GPL on August 19, 2005 (the engine only, not the textures or models). Quake III Arena on Wikipedia
The browser version
Q3JS is a multiplayer Quake III Arena experience for the browser, built and maintained by LK. Its README calls it "built on ioquake3 and WebAssembly". It comes with a browser client, packaged dedicated servers, a WebSocket-to-UDP gateway, server discovery and player statistics.
The site opens on a server browser you can search by server, map or player, with filters for featured, populated and open-slot servers, plus a Quick Play button. Around it sit a global frag feed, fragger leaderboards (24 hours, week, month and all time), a scoreboard, a weapon database, player stats, voice chat, a phone mode and a guide for running your own server.
On game data: the hosted site relies on officially released demo data. The README adds that Q3JS does not include or download proprietary Quake III data, and that anyone running their own copy supplies PK3 files themselves.
pieter.com hosts a Quake 3 server at q3.pieter.com that its own page says is powered by Q3JS. LK has two sister projects, Counter-Strike 1.6 at csjs.live and Jedi Academy at jk.q3js.com. Q3JS calls itself a non-commercial fan project with no connection to id Software or ZeniMax.
| Method | Open-source engine (ioquake3) compiled to WebAssembly |
|---|---|
| Renderer | OpenGL 2 |
| Game data | The hosted site uses officially released demo data. You supply your own PK3 files to run a copy |
| Multiplayer | Live server browser, Quick Play, custom servers |
| Licence | Engine part GPL-2.0. The Q3JS client, server and site code are listed as proprietary in the README |
How to play it
- Open q3js.com in a desktop browser.
- Pick a server from the browser, or press Quick Play.
- Play. To run your own server, follow the guide linked on the site.
Links
Source code
Questions
Can you play Quake 3 in a browser?
Yes. Q3JS runs Quake III Arena multiplayer in a browser tab: open q3js.com and join a live server.
Is it recompiled or decompiled?
Neither, strictly. id released the engine source under the GPL and the ioquake3 project maintains it, so Q3JS compiles that source to WebAssembly. People search it as "Quake 3 recompiled" and "decompiled" for the same thing.
Do I need to own Quake III Arena?
Not for the hosted site, which uses officially released demo data. If you run your own copy of Q3JS you supply your own PK3 files.
Does it work on a phone?
The site advertises a phone mode.
Is it official?
No. Q3JS is a non-commercial fan project that says it has no connection to id Software or ZeniMax.
Sources and coverage
Details checked 2026-10-08. Fan projects change fast; check the project page for the latest.