The tuner takes the microphone signal into the Web Audio API and reads the raw waveform with an AnalyserNode. On each frame it runs an autocorrelation (the well-known ACF2+ method): it checks the signal level to ignore silence, then compares the waveform with delayed copies of itself to find the lag at which it best repeats — that lag is the period of the note, and the sample rate divided by the period gives the frequency in hertz. Parabolic interpolation around the peak refines the period for sub-cent accuracy, and a short median plus exponential smoothing steadies the readout. The frequency is then converted to the nearest equal-tempered note (A4 = 440 Hz) and a cents value, so you see exactly how flat or sharp you are. All of this runs locally in your browser.

You can choose standard guitar tuning (E2 A2 D3 G3 B3 E4), Drop D (low E down to D), half-step down (every string down a semitone), Open G (D G D G B D), Open D (D A D F# A D), the modal DADGAD tuning, 4-string bass (E1 A1 D2 G2) and standard GCEA ukulele. With a tuning selected, the tuner highlights the string nearest to what you are playing and marks it with a green check when it is within ±5 cents, so you simply work string by string. Chromatic mode drops the string targets and instead shows the nearest of the twelve chromatic notes, which is handy for capos, alternate tunings not in the list, or tuning other instruments like violin, mandolin or a wind instrument.

Everything happens on your device. The microphone stream is processed live by the Web Audio API to estimate pitch, and the raw sound is turned into a note reading on the spot — there is no server, no account, no audio file and nothing is stored or transmitted. The browser asks for microphone permission only so the tuner can listen, and the mic is released as soon as you press Stop tuning or leave the page. Because the work is done in JavaScript in your browser, the tool also keeps working offline once the page is cached.

Pitch detection is most reliable with a clean, single note. If several strings ring at once, the room is noisy, or a string is buzzing or dead, the algorithm can briefly lock onto a harmonic and report the octave above or a neighbouring note. Very low bass notes also have long periods that are harder to resolve. The fix is simple: tune one string at a time, let the note ring clearly, reduce background noise and talking, and watch for the reading to stabilise before trusting it. For a loud stage or a critical studio setup or intonation job, a clip-on or pedal tuner that senses string vibration directly will be steadier than any microphone tuner — this tool is built for fast, accurate everyday tuning and practice.