Besides the websocket, the protocol has a couple of HTTP endpoints, you can see commands here: https://cs.chromium.org/chromium/src/content/browser/devtools/de

Besides the websocket, the protocol has a couple of HTTP endpoints, you can see commands here: https://cs.chromium.org/chromium/src/content/browser/devtools/devtools_http_handler.cc?q=devtools+agent+http&sq=package:chromium&dr=CSs&l=606 https://cs.chromium.org/chromium/src/content/browser/devtool... which looks like it ignores the HTTP verb and acts only on the path. I confirmed this with tests: fetch('http://localhost:9222/json/new' http://localhost:9222/json/new') and fetch('http://localhost:9222/json/new http://localhost:9222/json/new, {method:'POST', body:''}) do the same thing, as does using verb 'DELETE'. All these open a new tab. Without knowing a 128-bit target identifier, it looks like opening a new tab is the only thing you can do if someone is running DevTools.