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Frequently Asked Questions

How many CCU a Colyseus server can handle?

The maximum number of concurrent users (CCU) a Colyseus server can handle will vary accourding to how CPU-intensive your game loop is, and how much traffic your server is sending back to the clients.

The default "file descriptor limit" (amount of open connections you can have) of Linux servers is around 1024 - this value can be increased at your own risk. So, you can safely assume the cheapest cloud server is capable of holding 1024 concurrent connections. There are reports of people managing to have up to 600k open WebSocket connections, even though they're idle connections, without transferring data - it proves you can potentially handle more than 1024 concurrent connections by fine tuning the server specs and configuration.

I'm getting "Error: seat reservation expired", what does it mean?

This error originally means that the client was not able to effectively connect with the server's room in time.

This error may appear in a few scenarios:

  • Server is under heavy load and by the time it can respond to a WebSocket connection request, the "seat reservation" code has already expired. You may increase the seat reservation time limit to remedy this.
  • You have mixed Colyseus package versions in your package.json. (between 0.14.x and 0.15.x, for example) Make sure to only use packages under 0.15.x (if you are using version 0.15), OR 0.14.x (if you are using version 0.14) - the exact patch version does not matter, but major and minor matters.
  • When using multiple Node.js processes, your scalability configuration may not be correct. Make sure to follow scalability instructions.

Why is my room state not synchronizing with the client?

If you are using TypeScript to target ES2022/ESNext, you need to provide "useDefineForClassFields": false on your tsconfig to make sure @type() decorators are defining property accessors property.

  "compilerOptions": {
    "useDefineForClassFields": false,
    // ...

More info

For more information please check colyseus/colyseus#510

How can I sync data of the state only to a specific client?

You can either use schema filters, and/or send data manually to each client through room's send method.

Does Colyseus help me with client-prediction?

Colyseus does not provide any client-prediction solution out of the box. Games such as and do not use any form of client-prediction. lerping user coordinates usually gives reasonable results.

I'm getting this error: Class constructor Room cannot be invoked without 'new'", what should I do?

Make sure you have es2015 or higher in your tsconfig.json:

    "compilerOptions": {
        // ...
        "target": "es2015",
        // ...
    // ...