snapin

A snap-in is a software component that extends a host application by providing additional functionality without altering the host’s code. The term is most commonly associated with the Microsoft Management Console (MMC) in Windows, where snap-ins supply administrative tools and views within a single, extensible console.

In MMC, a snap-in is implemented as a component object model (COM) module that registers with the host. When MMC starts, it loads the selected snap-ins and builds a navigable console tree. Snap-ins contribute nodes, result panes, and user interface elements such as property sheets and context menus. They can deliver management tasks, views, and actions for specific system components or services.

There are stand-alone snap-ins and extensions. Administrators add snap-ins to a console via the Add/Remove Snap-in dialog; the configuration is saved in a console file (.msc). Snap-ins may run in-process with MMC or in separate processes, depending on design and security considerations.

Development and deployment involve implementing MMC interfaces (for example, IComponentData, IComponent, IExtendPropertySheet) and registering the snap-in in the Windows registry under MMC SnapIns keys, allowing MMC to instantiate and host the component. Snap-ins enable centralized management of services, devices, directories, and other subsystems within a consistent interface.

While closely tied to MMC, the term snap-in is also used more generally to describe plug-ins that extend a software host with additional functionality in other applications.