Why does the reading jump between strings?

Because the detector is reporting the nearest target rather than the nearest note, so a string tuned far below its pitch can land closer to the string below it. Tuning roughly by ear first and then using the tuner for the last few cents avoids the confusion.

Is the microphone recording anything?

No. The audio is analysed frame by frame in the page and discarded immediately, and nothing is stored or transmitted. Stopping the listening control releases the microphone, which is the state worth leaving it in when you have finished.

What does autocorrelation do that a simpler method does not?

It finds the period of the waveform by matching the signal against a delayed copy of itself, which is robust on a plucked string where the harmonic content is rich and the fundamental is not necessarily the loudest component. Simpler methods that look for the strongest peak often report the second harmonic instead of the note.

Why is the green zone about five cents wide?

Because that is roughly where a sustained tone stops sounding out of tune. Tuning to within five cents of the target is comfortably in tune for playing, and chasing the last couple of cents on a guitar is usually defeated by the instrument's own intonation.

Can I tune to something other than standard pitch?

The targets are fixed at modern pitch, so a guitar tuned to an older reference will read consistently sharp or flat across all six strings. When that is the intent, use the chromatic tuner, which reports the note and the offset without assuming a reference.

Guitar Tuner

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Guitar Tuner listens through the microphone and tells you how far each string is from its target pitch. It is locked to standard guitar tuning, with a four string bass preset alongside it.

What is Guitar Tuner?

Start listening and play one open string at a time; the needle shows how far the pitch is from its nearest target and which string it belongs to.

The interface:

A switch between the six string guitar preset and the four string bass preset.
A listening control that starts and stops the microphone, with an error message if access is refused.
A needle sweeping fifty cents either side of centre, where the middle means in tune and the bar turns green when the reading is within about five cents.
A row of targets showing each string's name, its note in words and its frequency, with the one being played highlighted.

Detection is by normalized autocorrelation over a range from about forty to five hundred hertz, which covers the guitar's six open strings from the low E at about eighty two hertz to the high E at about three hundred and thirty. Autocorrelation works by comparing the signal with a delayed copy of itself and finding the delay at which they line up best, which is the period of the waveform; the normalization is what keeps a loud harmonic-rich pluck from being scored differently from a quiet one. The method is octave-safe, meaning that a strong second harmonic does not cause the reading to jump an octave, which is the failure mode most pitch detectors show on a plucked string. The cents figure is the distance from the target in hundredths of a semitone, so a needle at the centre means the string is within a few cents of its note and the bar turns green at that point. Audio from the microphone is analysed in the page and never recorded or uploaded, which is worth stating because a tuner is the one tool here that asks for a live input. Playing a single string cleanly is what makes the reading stable; two strings sounding together give the detector two periods at once to choose between.

Where it is limited:

Guitar and four string bass only, so other instruments need the chromatic tuner.
A noisy room can make the reading wander, since the detector has no way to know which sound was intended.
The note readout is the nearest target rather than the nearest note, so a string tuned far out can read as its neighbour.
No reference other than modern pitch.
Nothing is recorded or stored.
No alternative tunings, so a guitar in an open tuning reads against standard targets.

Use it for the job it was named after: bringing a guitar or a bass to standard tuning before playing, checking an instrument that has been sitting in a case, or confirming which string is out. When the instrument is not a guitar or a bass, or the tuning is not standard, the instrument tuner works chromatically and includes presets for ukulele, violin and cello, which is the right tool for anything outside those two instruments. A tuner is the one place where a small amount of technique changes the reading more than any setting: letting a note ring rather than plucking repeatedly, and playing as close to the instrument as the microphone allows, gives a steadier figure than any adjustment to the controls.

How to use Guitar Tuner

Allow microphone access and start listening.
Play one open string and let it ring without touching anything else.
Read the needle and the string name, and adjust the peg until the bar turns green.
Move through all six strings, then check the first one again.

When to use Guitar Tuner vs related tools

Guitar Tuner is the tool to reach for when the instrument is a guitar or a bass in standard tuning, because naming the string is faster than naming a note. Instrument Tuner works chromatically and covers ukulele, violin and cello as well. When the target frequencies need checking rather than sounding, Note Frequency Calculator gives them, and Cents Calculator quantifies how far a reading is from where it should be.

Privacy & Security

This tool runs entirely in your browser — no data ever leaves your device. There is no server round-trip, no upload, no logging, and no account required. Your input is processed locally using client-side JavaScript and is never stored, transmitted, or accessible to anyone else. When you close the tab, everything disappears.