About this guitar tuner

A small, dependency-free page for one job: telling you, in real time, how close a plucked string is to the note it should be — no app, no cable, no account.

Why it exists

A phone or laptop already has a microphone, and a browser tab is faster to reach for than installing a tuner app or digging out a clip-on unit. This page needs no install and no account: open it, click Start, pluck a string, and read the note, the frequency and how far off it is.

How the pitch detection is computed

Once getUserMedia returns a stream, it is connected to a Web Audio AnalyserNode with an FFT size of 4096 — large enough to hold several full cycles of even the lowest string this tool targets (D2, about 73Hz) at a typical 44100Hz or 48000Hz sample rate. Roughly once per animation frame, the tool reads that window of raw time-domain samples and runs a difference-based autocorrelation over it:

For each candidate lag (a number of samples), the tool measures how closely the waveform matches a copy of itself shifted by that lag. A perfectly periodic signal matches almost exactly at a lag equal to one full period (and at its multiples); the tool looks for the first strong match as that lag increases, rather than continuing on toward a taller match at a multiple of the true period, which would report a whole octave incorrectly. Parabolic interpolation across the three measurements nearest that peak then refines the estimate between whole-sample lags.

Sample rate divided by that refined lag gives a frequency in Hz. The frequency is converted to a note using standard equal temperament (A4 = 440Hz, MIDI note 69; every other note's frequency is 440 × 2^((n − 69) / 12) for MIDI note n), and the deviation from the nearest semitone is expressed in cents — 100ths of a semitone — which is what positions the needle. A buffer whose root-mean-square amplitude is too low to be a real signal is treated as silence rather than guessed at, and the readout applies light exponential smoothing so a single noisy frame doesn't visibly jerk the needle.

How the site is built

Static HTML, one small stylesheet, one small script. No framework, no build step, no bundler.
Nothing about your audio leaves your device. There is no recorder, no upload endpoint, and no analytics beacon on this page for it to reach even by accident.
System font stack. Your operating system's UI font, so nothing has to download and nothing shifts as the page loads.
Dark mode follows your system setting via prefers-color-scheme.
The microphone is released deterministically. Clicking Stop stops every audio track and closes the AudioContext; the same happens automatically if you navigate away or close the tab.

Scope and honesty about limits

This is a genuinely useful tuner for practising at a desk, not a replacement for a calibrated clip-on or pedal tuner. A hardware tuner reads the instrument's own physical vibration and is largely unaffected by background sound; a microphone cannot be — a fan, music, conversation or a TV in the room competes with the string's pitch and can visibly disturb the reading, especially on the lower, slower-vibrating strings. Multiple strings ringing together, a buzzing fret, or a microphone positioned far from the instrument all reduce accuracy further. Treat a borderline reading as "close, verify by ear" rather than an exact measurement, and expect the low strings to take a moment longer to settle than the high ones purely because their vibration is slower to begin with.

The tuning presets (Standard, Drop D, Half-step down, Open G, DADGAD) cover six-string guitar only; there is no bass or ukulele preset, though the underlying pitch detector will still report a frequency and nearest note for any pitched instrument.