What key is my song in?
Type the chords in the order you play them. The key finder names the key, writes each chord as a Roman numeral, and points out chords that come from outside the key.
How it decides
Every major key has seven chords that belong to it: in G major those are G, Am, Bm, C, D, Em and F#dim. A minor key uses the same notes from a different home base — E minor shares G major's chords — and often borrows a major V chord (B or B7 in E minor) to pull back home.
The key finder checks your chords against all 24 major and minor keys, rewards chords that fit, and gives extra weight to the chord the song starts and ends on, because that is usually home. When two keys fit equally well — most often a major key and its relative minor — it tells you both.
Reading the numerals
Uppercase numerals are major chords, lowercase are minor, and ° is diminished. I–V–vi–IV in G is G–D–Em–C; the same numerals in C are C–G–Am–F. A ♭VII (F in G major) is borrowed from outside the key — common in rock, and nothing is wrong with it.
Write it with the whole band
Cobander is free songwriting and recording software that keeps your band on the same song: everyone records and writes from their own computer through the folder you already share, with chords, lyrics and structure on one timeline — and the band levels up as you go.
Free — the whole app, every song, forever. Windows and Mac. More about Cobander.
Questions
Why does it say two keys?
A major key and its relative minor use the same chords. Listen for which chord feels like home — that is the key.
What about power chords?
Power chords (G5) have no major or minor third, so they fit either way. The key finder uses the others around them to decide.
Can it hear the key from a recording?
Not in the browser. The Cobander app hears the key from your band's recordings.