Song key finder

What the key tells you

• Which chords fit: in C major they are C, Dm, Em, F, G and Am, so you can play or write along.
• Whether a song suits your voice: if the chorus sits too high, sing it two or three semitones lower.
• What mixes well: DJs pair songs whose Camelot codes match or sit one step apart.
• Where to go next: the relative minor of a major key shares its notes and gives a darker verse or bridge.

Major or minor

Major and minor keys built on the same notes sound bright and dark respectively. The finder compares how much the song uses each of the 12 notes with the pattern of every major and minor key, 24 in all, and reports the closest match. When a major key and its relative minor score almost the same, the result says it is less sure, and the relative key is shown next to it.

When the key is hard to pin down

• Songs that change key: the finder reads the middle two minutes and reports the main key.
• Modal songs, such as Dorian or Mixolydian ones, are reported as the nearest major or minor key.
• Rap, drum tracks and spoken parts carry little harmony, so the key comes back as uncertain.
• Detuned recordings, such as old tapes, can read a semitone off.