To help us with aspects like linting, security or style, many of us have Rubocop analyzing our code. It's a very useful tool that is widely used, easy to set up and configure. Rubocop can even automatically auto-correct your source code as needed. How is this even possible? It turns out that Ruby is really good at taking Ruby code as input and doing various things based on that input. In this talk, I will go through some of the internals of Rubocop to show how it analyzes and makes changes to your source code.