NetWm

NetWM, short for Net Window Manager hints, is a specification for communication between X Window System clients and window managers. It defines a set of window properties and conventions that let applications describe their state and requirements to the window manager, which then controls decorations, placement, stacking, and desktop assignment. NetWM is a foundational component of the X11 window manager hints and is closely related to ICCCM. Extensions, especially the Extended Window Manager Hints (EWMH), build upon NetWM with a broader set of _NET_WM_* properties for richer cross-desktop interaction.

Key properties include _NET_WM_NAME and _NET_WM_VISIBLE_NAME for titles; _NET_WM_DESKTOP for desktop assignment; _NET_WM_WINDOW_TYPE to classify window kinds (normal, dialog, dock, menu, etc.); _NET_WM_STATE for states such as maximized, fullscreen, sticky, above; _NET_WM_PID for the process ID; _NET_WM_ICON for window icons; _NET_WM_STRUT and _NET_WM_STRUT_PARTIAL to reserve screen space for panels; _NET_WM_ICON_NAME and _NET_WM_ICON_GEOMETRY for icon details. The root window can advertise supported hints via _NET_SUPPORTED and _NET_SUPPORTING_WM_CHECK, helping clients adapt.

Most modern X11 window managers and toolkits implement NetWM or EWMH support. WMs such as Openbox, i3, KWin, and Mutter rely on these hints to coordinate decorations, focus, and desktop control; GTK and Qt toolkits also emit or consume _NET_WM properties. While widely supported, some properties are optional or inconsistently implemented across environments, and NetWM remains a pragmatic, extensible standard rather than a rigid protocol.