Q3JS is a non-commercial fan project that brings Quake III Arena to web browsers, letting players join multiplayer matches without installing the game. Built with WebAssembly and a GPL-licensed build of the ioquake3 engine, the project uses officially released demo data and is designed, built, and maintained by L K. Q3JS is not affiliated with id Software or ZeniMax.

The site offers a server browser where players can search for servers, maps, or players, review available arenas, and join matches. Players can also explore live arena activity, view a global frag feed, and check rankings across periods including the past 24 hours, the week, the month, or all time. Additional features include a scoreboard, player statistics, voice chat, a weapon database, and support for custom servers. Users can also run a server and access the project’s source code on GitHub. Q3JS presents browser-based multiplayer as a quick way to revisit the classic arena shooter, with related browser games such as Counter-Strike Classic and Jedi Academy also featured on the site.