Infocus

Infocus is a Chrome extension that keeps you focused while you're on the internet. You can input sites that you find distracting (eg. YouTube, Facebook) and Infocus will automatically stop you from visiting these websites by either going back to the previous page, or closing the tab entirely if it is a newly opened tab.

If you absolutely have to disable Infocus for something, you'll get to practice some mental math in the process!

Infocus is also open source: https://github.com/Anton-Cao/Infocus. If you have feature requests, feel free to open an issue in the GitHub repository!