Plugin

A software component that adds a specific feature to an existing computer program.

A plugin (also called an extension or add-on) is a software component that adds specific functionality to an existing application without modifying its core code. Plugins conform to the host application's defined extension points and APIs, allowing third-party developers to extend capabilities in a modular way.

Plugins are central to the extensibility model of many software tools, including IDEs (VS Code extensions), content management systems (WordPress plugins), and browsers (Chrome extensions). The plugin architecture allows the core application to remain lightweight while users add only the functionality they need.

In API gateway contexts, plugins extend gateway behavior with additional processing logic. Many API gateways support plugin systems for adding custom authentication methods, logging integrations, response transformations, and protocol translations. For example, an API gateway might offer plugins for JWT validation, OAuth token introspection, IP whitelisting, or request/response body modification. This plugin model allows teams to customize their gateway without forking or modifying the core gateway code.