What is a Grails plugin?

A plugin is a packaged, reusable unit of functionality that extends a Grails application — anything from adding new artifacts (controllers, domain classes, tag libraries) to hooking into the application's startup lifecycle or wrapping an entire external library behind Grails-friendly conventions.

Plugins are added as ordinary dependencies in the application's build file, and because Grails resolves them through the same convention-driven artifact scanning it uses for the application's own code, a well-built plugin often integrates as if its controllers, services, or domain classes had been written directly inside the application itself. Common examples include database migration support, Spring Security integration, and asset pipeline management for CSS/JS — each distributed and versioned as its own plugin rather than baked permanently into Grails core.

This plugin architecture is a big part of how Grails keeps its own core framework relatively focused while still offering a rich, opinionated ecosystem — features that not every application needs stay optional add-ons instead of permanent framework weight.