x11/xmon - The NetBSD Packages Collection

  Xmon interactively monitors the byte-stream connections
between an X server and a number of X clients.  Xmon
recognizes all requests, events, errors and replies sent
between the clients and the server which are part of the
core X protocol.  The contents of these messages are
displayed on standard output at a user settable degree of
detail from none to every bit and byte.  Xmon also allows
the user to select a number of requests or events to be
monitored at a different degree of detail.  Xmon will also
block the transmission of selected requests from the
clients to the server and selected events from the server
to the clients.  Xmon also keeps statistics of the number
of requests, events, and errors received.