MIDI Tools
If you use a Mac, check out the tools available at https://www.snoize.com/.
Command line tools:
Check out the fantastic tools created by Geert Bevin:
These two small tools are invaluable, and a must-have, if you do any kind of MIDI related development/debugging.
WebMIDI support
Check if your browser supports WebMIDI with studiocode.dev/check-webmidi.
MIDI Monitors
Other MIDI tools
https://www.snoize.com/MIDIMonitor/ MIDI Monitor is an app to display MIDI signals going in and out of your Mac.
https://www.snoize.com/SysExLibrarian/ SysEx Librarian is an app to let your Mac communicate with MIDI devices using System Exclusive messages, also known as SysEx. The most common use is to backup patch data from synthesizers, although there are others (such as sending firmware updates).
https://www.soundlib.com/studio/?p=mt Monitor the input of your MIDI controller
http://www.subtlesoft.square7.net/MidiPipe.html
http://notahat.com/midi_patchbay/ MIDI patchbay lets you hook up your various pieces of MIDI software and hardware and pass MIDI data between them, applying assorted filters on the way. Things like key splits, MIDI channel remapping, transposition, etc. are simple.
https://www.johanlooijenga.com/tools/
http://www.s-r-n.de/midile/ MIDI over Bluetooth and USB for iOS and OSX
https://www.morson.jp/pocketmidi-webpage/ Pocket MIDI is a MIDI monitoring tool for Windows and Mac. Connect your MIDI instrument to computer using a USB or USB/MIDI adapter and you can monitor MIDI messages to and from your instrument in real time. You can also send message from the application to your instrument. Pocket MIDI(for Windows/Mac) is a freeware.
https://osculator.net/ OSCulator is the missing link between your controllers and your music or video software. For example, you can use your Nintendo Wiimote or Apple iPhone with Ableton Live or any MIDI compatible application, with ease.
MIDI miscellaneous
Setting Up A MIDI Over Internet Session - How It Works - Using RTP MIDI OSX : https://sonicstate.com/news/2020/10/30/setting-up-a-midi-over-internet-session-how-it-works/