xprop

Display window and font properties in an X server. More information: https://manned.org/xprop.

• Display the name of the root window:

xprop -root WM_NAME

• Display the window manager hints for a window:

xprop -name "window_name" WM_HINTS

• Display the point size of a font:

xprop -font "font_name" POINT_SIZE

• Display all the properties of the window with the ID 0x200007:

xprop -id 0x200007