JVMetro provides a colorful, realtime visual indication of the passage of bars and beats on the Jack transport--without generating any sound of its own.
For simplicity, SDL is used to generate graphics.
It is often easier to use a visual metronome than to strain to hear a click track. Unfortunately, I couldn't find any such utility with an awareness of Jack.
There are no command line options and no GUI widgets. The JVMetro window can either be resized or closed. Tempo and bars-per-beats changes will be reflected automatically in the display. When the Jack transport is stopped, or in any other mode than timebase master, the display will be inactive and colored bright red. It is helpful if you tell your window manager to always keep JVMetro above other windows.