What Is the Rails Notes Command?

While reading through the Rails 6 changelog, I noticed an entry for a rails command called notes. Having never seen this before, I took a quick look at the Rails Guides.

The command rails notes will return a list of all instances of the following annotations in your codebase - FIXME, OPTIMIZE, and TODO.

You can optionally search for your own custom annotations with the --annotations (-a) flag:

rails notes -a NOTE
app/controllers/admin/blog_posts_controller.rb:
  * [10] [NOTE] Only return the last 10 blog posts

README.md:
  * [ 1] [NOTE] Set the following env variables

There's also a way to register your own custom annotations for use with the default runner

config.annotations.register_tags("DEPRECATEME", "TESTME")

Rails Guides - Rails Notes