A sample (or a small portfolio of sample) images would help people grasp what this does. Or a sample project.

(It’s not like it’s super-complicated, but people like pictures.)

This looks nice! Why don't the dividers snap to the closest edge automatically? Feels like that's a lot of manual labor that could just be done automatically.

Is there a way to output an SVG? I'd love to send this to my laser or CNC cutter and have it cut automatically.

You could let people post public inserts for specific games, start building up a library.