One of my litmus tests for software is "can I use it on a flight?", so you'll be pleased to know Subtrace works great locally without ever talking to subtrace.dev!

    subtrace run -devtools=/subtrace -- python3 -m http.server

Run the above command in a Linux machine, go to http://localhost:8000/subtrace and send some requests to localhost:8000 to see a stripped down version of the Subtrace dashboard working fully locally.