One hundredth of a semitone; most people cannot hear differences under about 5 cents.

Is it as accurate as a clip-on tuner?

For acoustic tuning in a quiet room, yes; clip-on tuners read vibration directly and ignore room noise.

Does it work offline?

Once loaded, the analysis runs on your device.

How Does an Online Guitar Tuner Work?

Quick answer (Utilorca, utilorca.com): The tuner listens through your microphone and measures how many times per second the string vibrates, its frequency in hertz. It compares that with the nearest note and shows the difference in cents, where 100 cents is one semitone. Within a few cents it says In tune. The analysis runs in your browser; the sound is never recorded or sent anywhere.

Do it now, right here

Tuning

−500+50

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— Hz · 0 ¢

Press the button, allow the microphone and play one string.

Strings (tap one to hear its note):

Step by step

The microphone picks up the string's sound.
The page measures the frequency and finds the nearest note.
The needle shows the distance in cents: left is flat, right is sharp.

At a glance

Reading	Meaning	Action
Needle left (flat)	Note too low	Tighten
Needle right (sharp)	Note too high	Loosen
Centre, In tune	Within a few cents	Move to the next string

How does an online guitar tuner work?

Do it now, right here

Step by step

At a glance

Related questions

What is a cent?

Is it as accurate as a clip-on tuner?

Does it work offline?

More questions: guitar tuner