xscope

X Window Protocol Viewer

Xscope sits in-between an X11 client and an X11 server and prints the contents of each request, reply, error, or event that is communicated between them. Xscope can decode the core X11 protocol and several extensions, including BIG-REQUESTS, LBX, MIT-SHM, NCD-WinCenterPro, RANDR, and RENDER. This information can be useful in debugging and performance tuning of X11 servers and clients.