Comment by superkuh

I haven't used it, but it works in a Docker container without any device mounting or access to the host X server, so I'd assume that it does indeed work without any X available.

I've played with it and it works over a headless server instance through an ssh session, so I think it does not require X11

It does work without an external X11 all right (trick question, actually, there's an Xvfb underneath all the turtles - so X11 actually is required, even though it's all hidden inside the container ;))