Roots and slash-bass notes are shifted; the chord quality (m, 7, maj7, sus4, add9…) is kept as-is. Non-chord tokens pass through unchanged, so it works best on chord lines rather than full lyric sheets.

Clamp the capo on the given fret and finger the chord shapes of the "play shapes in" key; it will sound in your song's key. The CAGED open keys — C, A, G, E, D (and their relative minors Am, Em, Dm, Bm, F#m) — need no barre chords.