GUIMIDI

Play your Mac's MIDI instruments from an on-screen piano.

Mac · In development · Not released

GUIMIDI's window on a Mac: a full 88-key piano keyboard, with a note display at the left of the title bar and Chord, Harmony, and Key menus at the right — GUIMIDI is a piano keyboard in a window. Click a key or type on your computer keyboard, and it sends the note to your music apps and MIDI instruments. GUIMIDI makes no sound itself.

About

GUIMIDI lets you play a note or a chord without a hardware keyboard. You can use it to try out a synth, test a MIDI setup, or play a backup part with one finger. Your music apps see it as a MIDI input, and it also appears in Audio MIDI Setup, so you can cable it to your other instruments.

What it does

Shows all 88 piano keys, from A0 to C8, and fewer keys around middle C when the window is narrow
Plays from the mouse and from the computer keyboard, with up to 8 notes at once
Keeps playing from the computer keyboard while another app is in front, if you give it Input Monitoring permission in macOS
Plays a single note or one of 15 chords from each key, including major, minor, sus, sixth, and seventh chords
Chooses each chord from your song's musical key, with Nashville, blues, and jazz chord rules
Offers smooth voice leading, an added bass note, and snapping to the musical key
Shows the note and octave being sent on a red LED display in the title bar
Sends channel aftertouch that rises while you hold a key
Sends on the MIDI channel you choose, from 1 to 16
Resizes with the window, runs full screen, and keeps its Chord, Harmony, and Key menus in the title bar

GUIMIDI with Nashville Triads in the key of G: one pressed key plays a G major chord, and the note display reads G 4 — With a harmony on, each key plays the chord that belongs to it in your song's musical key. Here, the G key plays G major in the key of G.

Requirements

GUIMIDI needs macOS 13 or later, and a music app or MIDI device to play the notes. It has only been run on macOS 27, on a Mac with Apple silicon. It hasn't been tested on earlier versions of macOS or on Intel Macs.

Privacy

GUIMIDI works entirely on your Mac and makes no network connections. To play while another app is in front, it asks for Input Monitoring permission and reads the key code of each key press to choose a note. It doesn't read the text you type, and it doesn't store or send your keys. You can turn this off in Settings.

User manual

GUIMIDI user manual (PDF): connecting to a DAW or synth, Input Monitoring, every control, and troubleshooting. All manuals are on the documentation page.

Availability

GUIMIDI is in development and not released. There's no release date yet. To hear if that changes, email [email protected].