The MIDI Monitor2 Audio Unit allows watching and analyzing incoming MIDI data streams, if plugged in as an instrument inside Audio Unit hosts.
The manual is shipped with the distribution app.
Note: The embedded Audio Unit, requires host applications, which can route MIDI messages. It is intentionally implemented as an Instrument, NOT as a MIDI effect.
With the main app you also may load MIDI files, listen to it and watch the MIDI flow. It has Core MIDI (MIDI IN and Out ports) connectivity therefore.