What key is this song in?
Drop in a track and find out what key and scale it is in, with the working shown.
Every key is just a set of notes with one of them treated as home. So finding the key of a recording means two things: working out which notes it actually contains, and then working out which of them is home. The first is arithmetic over the sound. The second is a judgement, and this page shows you the evidence for it rather than only the verdict.
What it tells you
- The key and scale — for example C major or F♯ minor — out of all twenty-four.
- How clear the answer is, because not every piece of music has one.
- The runner-up, and whether it is the relative major or minor.
- Every pitch the recording contains, added up regardless of octave.
- The score each candidate key was given, so you can see how close it was.
What people use it for
- Transposing a song into a range you can actually sing.
- Picking a backing track or a sample that will sit in the same key.
- Working out what scale to solo in over a track.
- Harmonic mixing, where the next record has to share notes with this one.
- Checking a recording that was sped up or slowed down and is no longer at concert pitch.
Where it struggles
- Music that changes key partway through has no single right answer.
- A drum loop or spoken word has no harmony to read in the first place.
- Heavily distorted or very sparse recordings give thin evidence.
- Relative majors and minors share every note, so the two are easy to swap.
Questions
How does it work out the key?
It measures how much of each of the twelve pitch classes the recording contains, then compares that profile against what each of the twenty-four keys is known to look like. The reference profiles come from Krumhansl and Schmuckler, who built them from an experiment in the early eighties where listeners rated how well each note fitted an established key. It is still the baseline that newer methods are measured against.
How accurate is it?
On ordinary tonal music with clear harmony it is usually right, and where it is unsure it says so rather than guessing confidently. The honest framing is that a key is a judgement about emphasis, not a property you can measure off the waveform, so treat a result marked ambiguous as a suggestion and trust your ears over it.
Why does it sometimes name the relative minor instead?
Because A minor and C major contain exactly the same seven notes. Nothing in the notes themselves separates them — only which note the music keeps returning to and rests on. When that is the runner-up, the page says so explicitly, because it is the one confusion worth knowing about.
Does it find the tempo or the chords too?
Not yet. This answers the key and shows the note content behind it. Chord detection and tempo are separate problems with separate failure modes, and bolting them on quietly would make all three less trustworthy.
Is my music uploaded?
No. There is no upload endpoint on this site at all. The track is decoded and analysed inside the page, and unlike the separation tools there is not even a model to fetch — this is arithmetic over a spectrum, so it works with the network off.
What files can it read?
Anything your browser can decode: MP3, WAV, M4A, AAC, FLAC, OGG and OPUS, and the audio track of a video file if you drop one of those in instead.