How the AI coach works

The Strumly coach is a chat interface backed by a large language model, a set of purpose-built tools, and a memory layer that persists between sessions. This page explains each piece — including what the coach can't do — so you know exactly what you're working with.

The conversation layer

When you open a session, the coach greets you with a specific suggestion drawn from your profile and recent sessions — not a generic "what would you like to work on today?" It's instructed to open with something concrete: "Last time your G→C change was landing late at 80 BPM. Want to push to 90?"

From there it works like a conversation with a teacher. You can ask questions about theory, technique, or gear; ask it to explain why a drill matters; or tell it to change direction. The model behind the coach can render things inline in the chat rather than just describing them:

• Chord diagrams — fingering charts drawn directly in the conversation.
• Drill cards — interactive chord-change drills with a target tempo, scored live by the audio engine.
• Practice plans — structured plans with labeled items and durations you can save.

The drill engine: how scoring actually works

When the coach starts a chord-change drill, your browser asks for microphone permission and the audio engine takes over. Here's what it does, concretely:

1. Your playing is captured by the microphone and analyzed locally, in your browser, by a web worker. The raw audio is not uploaded anywhere.
2. The engine computes a chromagram — a running measure of how much energy your signal has at each of the twelve pitch classes — and matches it against chord templates to detect which chord you're playing and with what confidence.
3. A scorer clocked to the target BPM checks whether you landed the target chord within a timing window (±120 ms by default) of each target beat.
4. When the drill ends, the results — success rate, timing score, and the millisecond offset of each transition (positive means late, negative means early) — are sent to the coach and saved to your session history.

The coach then reacts to the actual numbers. If you hit 4 of 8 transitions and every miss was late, it will tell you that, and what it usually means (your fretting hand is forming the shape after the beat instead of during the previous one).

The important privacy detail: only the scores leave your device. The audio analysis happens in-browser.

The memory layer

Two kinds of memory persist between sessions:

Your profile — skill level, goals, gear, weak spots, strong spots. The coach updates this as it learns things about you. Mention that barre chords buzz on the high strings and it records that as a weak spot; three weeks later it will still know.

Session summaries — when you end a session, the coach writes a summary of what you worked on and a specific focus for next time. The next session starts from that summary. This is the mechanism behind "picks up where you left off" — it's not a marketing phrase, it's a database row.

Memory works on the free tier. The 3-session monthly cap limits how often you can start a session, not what the coach remembers.

What the coach can't do

Honesty about limits matters more in coaching than almost anywhere else:

• It can't see you. No camera input. It cannot check your posture, wrist angle, thumb position, or fretting-hand shape. If your technique problem is physical, the coach can describe correct form and infer problems from your scores, but it cannot watch you and catch it directly. A human teacher still wins here — see our honest comparison.
• Scoring covers chord changes. The drill engine detects and scores chord transitions against a beat grid. It does not grade your bends, vibrato, tone, or dynamics.
• It's a language model. It's strong on theory, practice structure, and reacting to your drill data. Like any language model it can occasionally state something with more confidence than it deserves. For songs in Strumly's verified dataset, the coach is fed ground-truth chords, tuning, and capo data to keep it from guessing.

Try it

Open the coach (sign-in required — 3 free sessions a month), or start with the free tools and come back when you have a specific goal. The coach is at its best when you arrive with something concrete to fix.