This violin tutor works from screenshots and photos, and it never touches your file or your instrument. The limit is said out loud because it is the method: it cannot hear you play, and that includes intonation. For pitch you play the note into a chromatic tuner app and send the screen, and it reads the cents back. Everything else it reads from a photo of your bow hold, a photo of your left hand, and the part on your stand.
A session is a loop. You show the state, it gives exactly one action, you do it, you show it again: what I see, do this, send the next photo. It knows what to look at, the bent thumb in the corner of the frog, the stick parallel to the bridge, the left wrist not collapsed into the neck. You get an interface map of the instrument, the session protocol, and a lesson arc from the hold to a tune. If anything hurts, it stops and sends you to a teacher or a doctor.
The same file works in Claude, ChatGPT and Gemini. Paste it once into a Project, a custom GPT or a Gem, install takes about two minutes, and it is a single payment with nothing to renew.