Scalafix is rewrite and linting tool for Scala. There’s a continuous process of adding new rules that help enforce best functional programming practices. I will show how the most important rules work and how they were implemented. I will also share my experience porting Wartremover rules to Scalafix and compare the two. In this talk, you will learn how to implement a scalafix linter rule, from idea, implementation, testing and release. There will be also a few words about what Scalafix currently can and can’t do and what kind of problems it solves.