xwininfo

Xwininfo is a utility for displaying information about windows. Various information is displayed depending on which options are selected. If no options are chosen, -stats is assumed.

The user has the option of selecting the target window with the mouse (by clicking any mouse button in the desired window) or by specifying its window id on the command line with the -id option. Or instead of specifying the window by its id number, the -name option may be used to specify which window is desired by name. There is also a special -root option to quickly obtain information on the screen's root window.