MIDI Sequencer

A small MIDI loop recorder for the AKAI MPK mini play 3. It records what you play, loops it back through the MPK's internal sounds, and lets you overdub layers. You do not need a DAW.

The app also runs an MCP server, so an assistant such as Claude can control the transport, read the recorded loop, and export it.

Requirements

• Windows 10 or 11
• A Rust toolchain to build the app
• An AKAI MPK mini play 3 on USB (any other MIDI device also works)

Build and run

cargo run --release

The executable is target\release\midi-sequencer.exe.

Run in the background

midi-sequencer.exe --headless

With --headless the app opens no window. It keeps the MIDI ports connected and serves MCP until an MCP client calls quit. A second headless copy exits at once, because the first one holds the server address. The sequencer-panel Claude Code mod draws the controls in a pane and starts the app this way.

Usage

1. Plug in the MPK. The app connects to its input and output within two seconds.
2. Press Record (or R) and play. Every pass through the loop overdubs a new layer.
3. Press Space to stop and start playback.
4. Press Export .mid to write the loop into Documents\MidiSequencer.

Control	Effect
BPM, Bars	Set the tempo and the loop length in 4/4 bars.
Metronome	Plays a side stick on the drum channel on every beat.
MIDI out	Chooses where the notes play. PC soundcard (GS Wavetable) plays them through your speakers.
MIDI thru	Forwards what you play to the output. It turns on by itself for every output except the MPK.
Undo last take	Removes the notes of the latest recording pass.
Clear	Removes every note.

The app records notes only. It ignores pitch bend and controller messages.

Play through the PC soundcard

Windows includes a General MIDI synth called Microsoft GS Wavetable Synth. Choose PC soundcard (GS Wavetable) under MIDI out to hear the loop and the metronome on your PC instead of the MPK. The app turns MIDI thru on, so you also hear your live playing.

• The synth adds about 100 ms of latency, so live playing feels a little late.
• The MPK still plays its own sound when you press a key. Turn its volume down to hear only the PC.

MCP server

The server listens on http://127.0.0.1:7391/mcp while the app is open. It accepts connections from the local machine only. The .mcp.json file in this repository registers it for Claude Code sessions that start in this folder.

Tool	Effect
get_status	Returns the transport state, tempo, loop length, position, and MIDI ports.
play	Starts playback from the first bar.
stop	Stops playback and recording.
set_recording	Turns overdub recording on or off.
set_tempo	Sets the tempo in beats per minute.
set_loop_length	Sets the loop length in bars.
set_midi_out	Switches the MIDI output, for example to the PC soundcard.
set_instrument	Selects a General MIDI instrument for one channel.
add_notes	Writes notes into the loop as one take, so Undo last take removes them.
get_notes	Returns every recorded note.
export_midi	Exports the loop as a .mid file and returns its path.
set_midi_in	Switches the MIDI input.
set_metronome	Turns the metronome on or off.
set_midi_thru	Turns MIDI thru on or off.
undo_take	Removes the notes of the latest take.
clear	Removes every note.
open_export_folder	Opens the export folder in Windows Explorer.
quit	Closes the app.

Versioning

This project follows Semantic Versioning. The public interface is the MCP server and the exported file format. CHANGELOG.md lists every release.

• Major: a change that breaks an MCP client. Examples are a removed or renamed tool, a removed or renamed argument or result field, and a changed server address.
• Minor: a backwards compatible addition. Examples are a new tool, a new optional argument, a new result field, and a new feature in the window.
• Patch: a bug fix that leaves the interface unchanged.

While the version is below 1.0.0, a minor release may contain breaking changes.

License

Copyright (C) 2026 Filippo Negroni

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.