The most useful APIs are simple and composeable. Omnipotent DSLs can be great, but sometimes we want to just write Ruby. We're going to look at the process of designing a new API for attributes and type casting in Rails 5.0, and why simpler is better. We'll unravel some of the mysteries behind the internals of Active Record. After all, Rails is ultimately just a large legacy code base. In this talk you'll learn about the process of finding those simple APIs which are begging to be extracted, and the refactoring process that can be used to tease them out slowly.