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What is this?

MIDI Monitor is a Mac OS X application for monitoring MIDI data as it goes in and out of the computer.

SysEx Librarian is a Mac OS X application for sending and receiving MIDI system exclusive (aka sysex) messages.

This is the source code for the two applications. You do not need any of this if you just want to use the apps. You need the source if you want to play with the code, customize the application, or use parts of the code in your own project.

The source code is Open Source under the BSD license. See LICENSE for the legal details.

The project is currently intended to be used with an up-to-date Xcode version, like Xcode 11.1 (with the MacOS 10.15 SDK). However, it has been reported to work with earlier releases, as old as Xcode 9.2. (If you need to run it on an earlier Xcode, try checking out older revisions.)

How to build

  1. git submodule update --init --recursive
  2. Open MIDIApps.xcworkspace with Xcode.
  3. Open Configurations/Snoize-Signing.xcconfig and change DEVELOPMENT_TEAM to the Team ID of your Apple Developer account. See the file for more details.
  4. In the "Scheme" popup menu in the toolbar, select either MIDI Monitor or SysEx Librarian.
  5. Build and run!

What's inside

Your source tree should look like this:

  • Applications
    • MIDIMonitor
    • SysExLibrarian
  • Configurations
  • Frameworks
    • SnoizeMIDI
    • SnoizeMIDISpy
  • Third Party
  • Updates

Applications/MIDIMonitor Applications/SysExLibrarian

The source for the two apps. The project files are MIDIMonitor.xcodeproj and SysExLibrarian.xcodeproj; open them with Xcode.

Both apps are Cocoa and are written in Objective-C.

The apps rely on the other frameworks, described below.


A framework containing code for dealing with CoreMIDI in a Cocoa app:

  • Finding MIDI devices, sources, and destinations
  • Creating "streams" of input and output data
  • Hooking them up to inputs and outputs
  • Parsing incoming MIDI data into separate messages

This framework is used by both apps. You can use it in your own apps as well.

The code is mainly Objective-C, with one ordinary C file.


This project builds two things: A CoreMIDI driver, and a framework.

The CoreMIDI driver can "spy" on the MIDI sent to any destination in the system by any app. (See the MIDIDriverEnableMonitoring() function in CoreMIDIServer/MIDIDriver.h for more details.) The driver can then pass the MIDI data to another application.

The framework is used by apps that want to spy. It manages the communication between the app and the driver, and provides the app with an easy way to install the CoreMIDI driver when necessary.

This code is currently only used by MIDI Monitor, but it could be useful in other contexts. MIDI Monitor contains some code to channel the "spy" MIDI data into the rest of the SnoizeMIDI stream system, so it acts just like any other MIDI source.

The driver is written in C++, and the framework is C and Objective-C. You should be able to easily use the code from an application.


Contains .xcconfig files used to coordinate build settings across all the Xcode projects.

Third Party, Updates

Contains the git submodule for Sparkle (the ubiquitous app-auto-update framework) and the server-side files to make it work.

If you don't see the Sparkle submodule, do a git submodule update --init --recursive.


Please contact Kurt Revis with any questions.

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