Reverse chord finder

A chord name is a compressed description of intervals. Take the lowest-sounding note as a reference, measure the distance from a candidate root to every other note in semitones, and the resulting pattern maps to a quality: root, major third (4 semitones), and perfect fifth (7 semitones) spell a major chord; flatten the third to 3 semitones and it becomes minor. Sevenths, suspensions, and extensions each add or replace one interval in that stack.

The same set of notes can carry more than one legitimate name. A, C, E, and G is Am7, but read from C it is C6 — identical pitches, different root. Convention resolves the tie with the bass: whichever reading puts the root in the bass usually wins, which is why this tool ranks bass-as-root matches first and lists the alternatives after. When the lowest note is not the root at all, slash notation records both facts at once — C/G is a C major chord with G underneath.

Symmetric chords push this further. A diminished 7th stacks minor thirds all the way around, so Bdim7, Ddim7, Fdim7, and G#dim7 are the same four notes; an augmented triad divides the octave into three equal major thirds. For shapes like these the finder shows every valid root rather than pretending one answer exists.