xev

Print contents of X events. More information: https://gitlab.freedesktop.org/xorg/app/xev.

• Monitor all occurring X events:

xev

• Monitor all X events of the root window instead of creating a new one:

xev -root

• Monitor all X events of a particular window:

xev -id window_id

• Monitor X events from a given category (can be specified multiple times):

xev -event event_category