Perfect Pitch is a tuner and a practice notebook for violinists, in one browser tab. It shows how far off you are in cents, remembers that across a whole passage, and keeps the pieces you are learning where you tune them. It installs to a home screen and works with no network.

_{06   ANYWHERE}

Turns sideways. Installs.

_{Nine octaves will not fit a portrait column, so the page turns itself.
Installed, it opens with no network at all.}

Bun is what the lockfile is for. Google Chrome is needed only for the end-to-end tests, which drive a real browser.

bun install
bun run dev

Open the app, press listen, and allow the microphone. That is the whole tuner — it needs no account and no configuration.

The notebook needs Firebase, because pieces are saved to an account and follow you between devices. Copy .env.example to .env.local and fill it in from firebase apps:sdkconfig WEB <appId> --project <projectId>:

VITE_FIREBASE_API_KEY=
VITE_FIREBASE_AUTH_DOMAIN=
VITE_FIREBASE_PROJECT_ID=
VITE_FIREBASE_STORAGE_BUCKET=
VITE_FIREBASE_MESSAGING_SENDER_ID=
VITE_FIREBASE_APP_ID=

These ship to the browser and are not secrets — access is controlled by the security rules below, not by hiding them. Without the file the tuner still runs; only signing in is unavailable.

_{The notebook's end-to-end tests sign in for real, so they need firebase emulators:start first.}

Pitch — one equal-temperament formula, anchored at A4 = 440 Hz.

frequency(midi) = 440 * 2 ** ((midi - 69) / 12)

Detection — the McLeod Pitch Method: the first strong peak of a Normalised Square Difference Function, not the tallest. That is what stops a bowed string's harmonics reading an octave high. Echo cancellation, noise suppression and gain control are all off; each one mangles a sustained tone.

_{One note at a time. Double stops waver between the two.}

Offline — precache the build, hashed assets cache-first, navigations network-first with the cached shell behind them. A Vite plugin stamps the file list in at build from what Rollup actually produced, so the worker's list cannot drift from the files that exist.

Storage — a piece belongs to its owner structurally, nested under their user id rather than tagged with it. The rules check the shape of every write too, so a compromised client cannot store arbitrary documents or exhaust the quota:

match /users/{uid}/compositions/{compositionId} {
  allow read, delete: if isOwner(uid);
  allow create, update: if isOwner(uid) && isWellFormed();
}

No audio, charting or PWA library. Detection, synthesis, metronome scheduling and the service worker are all first-party.

src/
├─ lib/          pitch, notation, practice, scoring
├─ hooks/        microphone, preferences, Firestore, install
├─ components/   key bed, readout, meter, editor
├─ routes/       tuner · notes
└─ sw.js         offline
e2e/             Playwright, against a real browser
docs/
├─ screenshots/  what is above
└─ superpowers/  a design doc per feature

Every feature here starts as a short design doc in docs/superpowers/specs/ and ends with tests that would fail without it. Both are worth more than the diff.

git checkout -b your-branch
bun run test && bun run typecheck && bun run lint
bun run e2e                      # firebase emulators:start, for the notes tests