VSCode has become a staple for many developers local environment. One of the reasons is the powerful extensions which can be run from within the IDE itself, from type checking to code auto formatting. Here we will take a look at an overview of VSCode and then dig into how the auto formatting works. The final task will be to build a small version of Prettier (or eslint — fix) which can run as a VSCode extension. The goal is to understand the mechanics at work inside this kind of extension and some key differences with other types of extensions.