Online category with WebSocket relay in js13kGames 2025

We’re introducing the Online category in js13kGames 2025 for all of you missing the defunct Server category we had in the past, and with the current approach any instance of a given single player game can now communicate with each other.

Some of you might remember the Server category we had running since 2013, until it had to be shut down in 2022, due to Heroku closing shutting down their free tier that we relied on for hosting.

Now, with Cloudflare joining as our Partners this year, we’ve decided to run a little experiment: allowing any games to exchange messages between players through a dedicated relay server.

Expand your game with multiplayer features or user-generated content. Build on top of a simple WebSocket relay and use it however you feel best augments your game.

Ben Allfree is our expert and judge in this category, so if you have any questions or issues make sure to ping him on our Discord. You might also check out his repository exploring a potential SDK we might use in the future.

You will be able to win some prizes as well: top5 entries will win CosmoPirates game licenses and top13 will end up with Web Maker Pro subscriptions.

Check out the Online category landing page for all the current details: how to use it and what’s allowed. Keep in mind this is an experimental category, so the rules can still change.