Key Chord Builder
Build the diatonic chords of a selected key and label every degree with its harmonic role.
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Result
About this tool
Pick a key and the page lists the diatonic chords of that key, with Roman numerals and the harmonic role of each degree.
Use it when you are writing or learning in one key and want the seven chords that belong there, not a guess at which key a song is in.
The list is the natural major or minor set. It does not add secondary dominants, modal mixture, or the chords a real song borrows.
Example. Selecting C major lists I tonic C major, ii supertonic Dm minor, iii mediant Em minor, IV subdominant F major, V dominant G major, vi submediant Am minor, and vii° leading/subtonic Bdim diminished.
Limit. Only the seven diatonic triads of major or natural minor are built, so seventh chords and modes other than those two never appear.