I wrote a similar tool to help my friend practice piano (being a software person who dabbles in music, seemed like a reasonable idea).

To make sure I was "barking up the right tree" (metaphorically), I also shadowed her for a few piano lessons from a professional. Boy was I wrong!!

It's not that teaching/improving technique via app would be impossible, more that the things involved were completely not what I expected. Lots of stuff having to do with curling her fingers the right way, "don't use that finger, use this other one", "You'll have an easier time if you X instead of Y" &c &c &c.

I still want to someday make a tool to help self-train at piano, but now I realize it's gonna involve a lot of computer vision, rigid body dynamics, and a whole mess of stuff.

Er, uh, I mean, thanks for that link! I have a DSP (audio and MIR specifically) background and... (huge paragraph removed)

I'll just say thanks again.

(and your GLASSTONE submission, 6 years ago, is also the sort of link I enjoy)

I typically use https://www.basicmusictheory.com/c-major-scale to look up scales when I forget. For me this is going to be a quicker & more fun reference manual

All that being said, don't sell your self short. You made a cool tool that makes your process easier and you deserve to be proud of that. :)

Just.. don't fall into the very common trap of thinking "I can build a machine that'll entirely replace $X!" ;-) We can build machines that make $X easier, and easier, and easier but eventually you want a human being there to direct things ;-)

This isn't a diss at ALL, and, full disclosure, I once instrumented a tennis racket ("What if there was a tennis racket that improved your tennis?") and recently started dabbling with the idea of using webcams to teach myself yoga. Note that I know nothing about either tennis or yoga. :)

Edit: Holy crap OP, you know how to SHIP! Impressive home page. I salute you.