You hum a note, and you want to know what it actually is. Or you're tuning a guitar without a clip-on tuner in reach. An online pitch detector does this in the browser: it listens through your mic, finds the frequency, and names the note. The whole setup is one permission prompt.
The part people trip on isn't starting it — it's reading it. The display shows three things at once: a note name, a frequency in hertz, and an offset in cents. Cents are hundredths of a semitone. A reading of "A4, +12 ¢" means you're twelve hundredths of a semitone above a true A. Close, but audibly sharp to a good ear.
Thirty seconds to set up, one article to read it right. Here's both.
Browsers only allow microphone access on secure pages, and only after you say yes. The permission is per-site. Granting it here doesn't grant it anywhere else.
1 – Open the pitch detector and hit Start listening.
2 – The browser shows a prompt near the address bar. Choose Allow. On a phone it appears as a sheet at the bottom of the screen.
3 – Play a note. If the level bar under the waveform moves, you're live.
If nothing happens, you probably dismissed the prompt at some point in the past. Click the padlock (or the sliders icon on mobile) in the address bar and flip microphone back to allowed. Then reload.
No steps here, just what the numbers mean.
The big letter is the nearest note, with its octave — A4 is the A above middle C. Under it sits the measured frequency in hertz. That's the physics; the note name is just the label closest to it.
The needle is the part that matters for tuning. Dead center means you're exactly on the note. Right of center is sharp, left is flat, and the scale runs to ±50 cents — the point where you're closer to the next note than this one. Within ±5 ¢ the readout turns cyan. For most instruments and most ears, that's in tune. Don't chase ±0.5 ¢ on a guitar; the act of pressing a fret bends the string more than that.
A pitch detector reads one note at a time. That's not a flaw of any particular site — monophonic detection is the deal everywhere. A few habits make readings lock instantly:
1 – Play a single, sustained note. Let a plucked string ring instead of picking again right away. The first 50 ms of a pluck is noise, not pitch.
2 – Get within about 30 cm of the mic, but do not sing directly into it at full volume. If the level meter turns red, you're clipping, and clipped audio reads unstable.
3 – Kill background music. The detector can't tell your voice from the song you're singing along to — it'll hear whichever is louder and confuse both.
Steady tone, reasonable level, quiet room. That covers ninety percent of "the tuner is broken" complaints.
Sometimes the display shows — instead of a note. That's the detector telling you it isn't sure. Under the hood it computes a clarity score, and below 88% it refuses to answer rather than print a guess. Silence, hiss, two notes at once, the tail end of a decaying string — all of those produce a dash. A tuner that always shows a note is showing you fiction some of the time. Fine for a toy. Bad for tuning.
Live mic isn't the only input. If you have an MP3 or WAV — a voice memo, a riff idea, a mystery sample — the File tab analyzes it without uploading anything.
1 – Switch to File and drop the audio in.
2 – Wait for the progress bar. A three-minute file takes a few seconds. You get a pitch-over-time chart, the median pitch, the range, and buttons to export CSV or PNG if you want the data itself.
Works best on solo material. A full mix with drums and bass gives you gaps instead of nonsense, which is the right way for it to fail.
The tool assumes A4 = 440 Hz because most of the modern world does. Orchestras often tune to 442. Baroque ensembles sit at 415. If you're matching one of those, change the A4 reference and every note and cent value recomputes around it. Playing along to an old recording that sounds "between notes"? This slider is usually the answer.