Plugins Folder

Plugins define behavior that is common to all the routes in your application. Authentication, caching, templates, and all the other cross cutting concerns should be handled by plugins placed in this folder.

Files in this folder are typically defined through the fastify-plugin module, making them non-encapsulated. They can define decorators and set hooks that will then be used in the rest of your application.

Check out:

The hitchhiker's guide to plugins
Fastify decorators.
Fastify lifecycle.