What key is
this song in?

It detects the pitched notes in the first 30 seconds of your recording, builds a histogram of which pitch classes dominate — weighted by how long and how hard each note is held — and matches that against the profiles of all 24 major and minor keys. The best match is the answer you see.

It works, but less reliably than on a solo instrument. The detector listens for pitched notes and vocals, guitars and synths all count — which usually still points at the right key, but a busy mix lowers the confidence. When the margin between the best and second-best key is thin, the result says so.

Relative keys — like C major and A minor — share the same key signature and nearly the same notes, so they're the classic ambiguity for any automatic key finder. When a song could honestly be either, we mark the answer low-confidence rather than pretend.

It analyses the first 30 seconds of music, after any leading silence. For most songs that's plenty — keys rarely change that early. If your song modulates mid-way, the answer reflects the opening key.

Free, and nothing is kept because nothing is sent — the audio is decoded and analysed entirely in your browser, on your device. Close the tab and it's gone.