RouteMIDI
RouteMIDI is a multi-platform command-line tool that makes it very easy to connect MIDI ports together, passing MIDI messages between them while filtering, transforming and converting them along the way.
All the heavy lifting is done by the wonderful JUCE library.
The project website is https://github.com/gbevin/RouteMIDI
RouteMIDI is the third member of a family of command-line MIDI tools, alongside SendMIDI (send MIDI messages) and ReceiveMIDI (receive and monitor MIDI messages). It deliberately shares their concise command vocabulary, number and note-name parsing, and JavaScript scripting, so if you know one of them, you already know most of RouteMIDI.
Purpose
RouteMIDI turns your computer into a flexible MIDI patchbay. It connects one or more MIDI input ports to one or more MIDI output ports, and lets you decide exactly which messages flow through and how they are modified on the way. Typical uses are merging and splitting ports, remapping channels, transposing a keyboard, scaling velocities, filtering out clock or aftertouch, or running arbitrary JavaScript on each message.
It can also be driven programmatically. RouteMIDI publishes a machine-readable command schema (--schema json) and includes a built-in Model Context Protocol server (--mcp), so scripts and AI assistants can discover the commands, start routes, and inspect or live-edit them while they run; see AI.md.
ShowMIDI
If you're looking for a beautiful GUI to effortlessly visualize MIDI activity without having to wade through log files, please take a look at my other tool ShowMIDI: https://github.com/gbevin/ShowMIDI
Download
You can download pre-built binaries from the release section: https://github.com/gbevin/RouteMIDI/releases
Since RouteMIDI is free and open-source, you can also easily build it yourself. Just take a look into the Builds directory when you download the sources.
If you're using the macOS Homebrew package manager, you can install RouteMIDI with:
brew install gbevin/tools/routemidiUsage
To use it, simply type "routemidi" or "routemidi.exe" on the command line and follow it with a series of commands. These commands have purposefully been chosen to be concise and easy to remember, so that it's extremely fast and intuitive to set up a MIDI routing.
These are all the supported commands: