Witchcraft is a Google Chrome extension for loading custom JavaScript and CSS directly from a folder on your local machine, injecting them into web pages that match specified URL patterns.
It works by matching every page domain against script file names available in the scripts folder. For instance, if one navigates to google.com, Witchcraft will try to load and run google.com.js and google.com.css.
For more information on how to install and use it, head to Witchcraft's home page.
See here.
Witchcraft is my rendition of defunkt's original extension, dotjs.
Images in the logo were provided by Freepik.