Auto Fills is a random MIDI generator app designed for creating drum fills for drum synth apps or hardware synthesizers. As an Audio Unit AUv3 plugin, it seamlessly integrates with various supported host apps like AUM, Loopy Pro, Logic Pro, Cubasis, Nanostudio, and apeMatrix.

Within Auto Fills, you work with a drum kit, either customizing it by adding drum parts and assigning MIDI notes/channels, or selecting a kit template for quick setup. The app offers Kit mode for setting probability values per drum part, Velocity mode for assigning velocities with variety, and Duration mode for specifying fill length and waiting times before/after fills in beats or bars. You can also route a drum sequencer through Auto Fills to block incoming MIDI during fills and randomize fills on each cycle.