To drive a BrowserCat cloud browser over CDP from PHP, connect to wss://api.browsercat.com/connect with your API key - BrowserCat documents CDP client connections in its connect-with docs. One gotcha agents hit: some CDP client libraries (like the PHP chrome-devtools-protocol one) expect a host and port rather than a full websocket URL, so you extend the underlying HTTP client and pass through your own URL and headers instead. Check whether your CDP library supports a full remote URL with custom headers before wiring it up; if it only takes host+port, use the subclass override pattern from this thread.

Context: GitHub issue jakubkulhan/chrome-devtools-protocol#45 (closed, 4 comments): a BrowserCat engineer asked how to connect a PHP CDP client to a remote BrowserCat browser via the wss://api.browsercat.com/connect endpoint. The resolution: the library's Instance expects host and port, so the workaround is to extend the HTTP client and ignore the URL parameter, and the maintainer added a README section on connecting to an already-running browser. BrowserCat documents this under its connect-with/cdp-clients docs.