It writes counterpoint. Give it a melody and it composes an independent second voice against it, following the rules of first-species counterpoint — note against note, all consonant, with a proper cadence.
Three ways: draw it on the timeline grid, import a MIDI or MusicXML file, or type it into the “Cantus as text” box. Leave a gap between notes to make a rest.
On a phone the grid opens in Scroll mode, so you can pan the page without accidentally editing. Tap the toggle above the grid to switch to Draw when you want to add or change notes.
Some melodies can’t support a legal first-species counterpoint — most often when the melody leaps into its final note instead of stepping to it. The readout names the rule and the note; nudging the last note or two, or flipping Above/Below, usually resolves it.
In modal keys (aeolian, dorian, and the like) it raises the leading tone at the final cadence for a firmer close. Turn it off for a pure, unaltered modal ending.
No. Contrapunctus is fully offline and requires no sign-in. It collects no data.
Tap Export — MusicXML for notation software, MIDI for a DAW — and choose a destination from the share sheet.
Requirements: iPhone or iPad running a recent version of iOS.