MIDI Monitor

Download Version 1.5.4

MIDI Monitor is an app to display MIDI signals going in and out of your Mac. Musicians will find it handy for tracking down confusing MIDI problems, and programmers can use it to test MIDI drivers and applications.

MIDI Monitor is free to download and use. The source code is available as Open Source, under the BSD license.

System Requirements



20 July 2023

  • Now requires macOS 10.13 or later. If you're using 10.11 or 10.12, use version 1.5.3 instead.
  • Fixed a crash when receiving large amounts of MIDI data by "spying" on the output of another app.

24 January 2022

  • Fixed a crash when saving documents with extremely large timestamps. (It was unlikely to encounter them in normal circumstances, but other apps could generate them by mistake.)

4 January 2022

  • In Full Screen mode, hiding or showing the Sources and Filters sections produced incorrect layout.
  • Fixed another crash when quitting the app or closing a window. (It happened only when the preference "Ask to save when a changed window is closed" and the system preference "Close windows when quitting an app" were both on, and the document was Untitled with changes.)

20 December 2021

  • Fixed a crash when quitting the app or closing a window. (It happened only when the preference "Ask to save when a changed window is closed" was off.)

18 December 2021

  • Now requires macOS 10.11 or later. If you're using an older version of macOS, use version 1.4.1 instead.
  • Modernized the code. Rewrote the app in Swift, and upgraded to newer APIs. This will improve reliability, and will make it easier to add new features. I want to keep MIDI Monitor working for another twenty years!
  • The app is now distributed as a disk image. This works better with macOS’s current security systems, and makes it easier to install the app by dragging to the Applications folder.
  • Detailed event data is now displayed using a view supplied by HexFiend, rather than plain text. It looks much nicer, and lets you copy the data as either hex bytes or text, not both mixed together.
  • Fixed a bug on Macs with Apple Silicon (aka M1 or ARM) processors: when many MIDI messages were received at the same time, we would display corrupted and invalid events.
  • Shows the full name of MIDI devices and ports, better matching other apps.
  • Updated SysEx manufacturer names and controller names.
  • Other small bug fixes.

8 November 2020

  • Updated to support macOS 11.0 "Big Sur" and Apple Silicon Macs.
  • Big Sur note: "Spy on output to destinations" will not work in 11.0 - 11.1. Update to 11.2 to fix it. (It was Apple's bug.)
  • New features:
    • Added a preference to automatically observe MIDI devices when they are added. (Thanks to Ben Stoneking.)
  • Bug fixes:
    • Fixed a bug that could cause MIDI Monitor to not install its driver at startup.

22 September 2018

  • Updated for macOS 10.14 Mojave, including Dark Mode.
  • Now requires macOS 10.9 or later. If you're using an older version of macOS, use version 1.3.2 instead.
  • Bug fixes:
    • Improved error handling when the driver can’t be installed or can’t be found.
    • Updated MIDI manufacturer names and IDs.
    • Show program changes as 1-128 or 0-127 depending on a preference.

1 September 2014

  • Fixed a bug: the spying MIDI driver would not work when an old 32-bit-only MIDI driver was also installed. (For instance, certain Roland and M-Audio MIDI drivers.)

20 August 2014

  • MIDI Monitor now auto-saves documents and automatically restores them on launch, like modern OS X apps do.
  • Fixed a bug causing "Untitled" documents to appear when they shouldn't have.
  • Don't warn when opening a document whose sources are not currently present. It's more annoying than helpful.
  • Show more details in the "data" line for sysex events. In "expert mode", show the raw bytes of the event. Allow viewing the detailed hex data for all kinds of events, not just sysex.
  • Modernized UI slightly: lists now fill the whole window.
  • Now requires Mac OS X 10.7 or later. If you're using an older system, use version 1.3.
  • Updated app signature so it launches without warning on Mac OS X 10.9.5.

3 September 2012

  • Fixed a bug: the "spying" driver wasn't being installed properly.
  • Added "expert mode" to display some messages more accurately.
  • Added automatic updating via Sparkle.
  • Built for 32- and 64-bit. No more messages about the MIDI Server having to restart in 32-bit mode.
  • No longer works on PowerPC or 10.3 or 10.4, sorry. If necessary, get version 1.2.5, which does.
  • Picked a better font for the long data views.

5 November 2011

  • Updated the list of manufacturer IDs.

10 October 2009

  • Fixed a bug introduced in 1.2.3: spying didn't work.

28 September 2009

  • Fixed a race condition in incoming MIDI processing, which could lead to a crash.
  • Updated the list of manufacturer IDs.

18 August 2009

  • Fixed a bug: in the sources list, some one-port MIDI interfaces did not have names.

29 March 2009

  • Fixed a bug: the "receiving sysex" spinner did not go away after short sysex messages were received.
  • Sysex messages from DSI devices are now shown as "Sequential / DSI" (since both Sequential and DSI use the same manufacturer ID).
  • New icon thanks to David Clark!

7 September 2008

  • MIDI events are now saved in documents.
  • Fixed an old and embarrassing bug with the disclosable Sources and Filters sections. They now work correctly when the window is nearly the size of the screen.
  • When new events are received, don't always scroll to the bottom, and show the events more quickly.
  • Fixed more cosmetic bugs: Source names would disappear when clicked, when running on Leopard. Selection highlight on the event list could get cut off. Disclosure button animation was flickery.
  • Simplified some threading code, which makes the app more stable, especially as MIDI devices are added and removed.
  • Updated the source code to work with Xcode 3.1.
  • Now requires OS X 10.3.9 or later. If you're still on 10.2, use the old version, 1.1.8.

22 January 2006

  • MIDI Monitor is now a Universal application. It is 100% native on Intel and PowerPC.
  • The source code has been updated to work with Xcode 2.2.

12 September 2004

  • MIDI Monitor is now open source!
  • Rewrote some code to remove dependencies on the Omni frameworks. This makes it easier for me to distribute the code, and easier for others to build the code. It also makes the application slightly smaller.
    • The downside: MIDI Monitor now requires Mac OS X 10.2 or later. I don't think this will be a hardship since most MIDI drivers and applications are now built for 10.2. If you need a version which runs on 10.1, download it here.
  • Fixed a bug which prevented external device names from appearing in the Sources section.