Online tuner

Choose Guitar, tap Start, allow the microphone and play one open string at a time. The tuner recognises the nearest string of standard tuning (E A D G B E) and tells you whether to tighten or loosen it; when the needle sits in the middle, “In tune” lights up. Bass, ukulele and violin have their own mode; for voice, horns or any other instrument there's chromatic, which reads every note.

440 Hz is the standard A and the one you start from: if you're not sure, stay there. Many orchestras tune to 442 Hz, and if you play with a piano or over a recording, their A is what counts, not the number. You can move the reference A from 415 to 466 Hz, one hertz at a time (415 is the baroque pitch), and go back to 440 with one tap.

No. The microphone only listens while the tuner is on, and the sound is analysed in the browser, on your device: nothing is recorded and nothing is sent anywhere. It closes when you tap Stop, when you leave the page or when you put it in the background.

A semitone is divided into 100 cents. The needle shows how many cents you are below or above the note, from −50 to +50: left is flat, right is sharp. Within 5 cents the note counts as in tune, a difference you can barely hear.