Reflect notes, not chord names
In C, this reflection exchanges C with G, D with F, E with E♭, A with B♭, and B with A♭; D♭ and F♯ also form a pair. C–E–G becomes G–E♭–C, the notes of C minor. The lines in the diagram connect each selected note to its partner. Applying the reflection twice returns to the original notes.
Try a dominant seventh
Search for G7 and choose it. Its notes G–B–D–F reflect to C–A♭–F–D. That collection can be named Fm6 or Dm7♭5, depending on the bass and context. Listen to both sets, then use the reflection to continue exploring. The tool names exact matches from the chord catalog; a collection without a match remains a custom chord.
Choose an axis and a voicing
The reference key sets the reflection axis. Major and minor use the same axis for a given tonic. The rule is (2 × tonic + 7 − note) modulo 12, with C represented by 0. Reflection operates on pitch classes rather than register, rhythm or fingering. Use the chord builder to choose a bass note and audition a close voicing; the reflected sound is an idea to try in context, not a required replacement.