eXtensions

An extension is a software component designed to add new features or modify the behavior of an existing application without changing its core code. Extensions extend the capabilities of the host program and can be installed or enabled by users to tailor functionality to their needs.

Extensions are common in web browsers, development environments, content management systems, and media players. They interact with the host through a defined extension API and run in a restricted or sandboxed environment to reduce security risks. The term is not always used consistently; some ecosystems call these components plugins, add-ons, or modules.

Development and packaging typically involve web technologies such as HTML, JavaScript, and CSS, bundled with a manifest or descriptor that declares permissions, APIs, and resources. Distribution is usually via official stores or marketplaces, and extensions may receive automatic updates from the platform.

Examples include browser extensions that block ads or manage passwords, content management system extensions that add SEO features or e-commerce capabilities, and IDE extensions that provide language support, debuggers, or code formatting. Similar concepts exist across platforms, though naming and APIs differ.

Security and privacy considerations are central to extensions, since they can access data within the host application. Best practices include installing from trusted sources, reviewing requested permissions, maintaining updates, and relying on the host platform’s security mechanisms such as signing and sandboxing.