This was kinda cool once I got it working! It reminds me of the terminal learn to type games.

I made an app to help learn chords and keys too: https://apps.apple.com/us/app/bloopkeys/id6689494178

Mine doesn't require MIDI (although it supports MIDI out as an option), but I can see why you went with that for yours.

Some notes/thoughts: 1. It didn't work on my iPhone (either with Firefox or Safari). 2. A helpful sentence or two would be useful. For example, it wasn't obvious that what you were looking for was midi in and not midi out. 3. Ignore the folks on here talking about monetization (it won't compete with something like Melodics). You made a fun little thing and that's great.