The web server is only active if you run the command fish_config. When you run this command, if finds the next available port, starting at localhost:8000 and opens a web browser pointing to that port.

Once in the web interface, you can click around to implement some pre-supplied recipies to your fish configuration.

If you hit ctrl-c, the fish_config program exits and stops listening on the port.

It's something you either run or you don't.