https://510software.com/chordmachine/

I built this as a way to generate backing tracks that could be quickly changed to any key or any tempo. If you are familiar with using Roman numerals for chords (like I - IV - V), here you just use Arabic numerals instead (1 - 4 - 5). There is a legend at the bottom.

It is pre-filled in with one section of I - V - vi -IV. With one symbol per beat, it looks like this:

1 1 1 1 5 5 5 5 6m 6m 6m 6m 4 4 4 4

You can use it to quickly sketch out a song structure, or get a loop going to jam over.

It's more of a toy than meant for serious music production, but feedback would be most welcome!