We already have a Plugin Index thread that lists all of the plugins developers have shared so far. It is in the sticky thread of our plugin sub forum here.
https://www.mobileread.com/forums/sh...d.php?t=247431
The plugin developer docs are here:
https://github.com/Sigil-Ebook/Sigil...ork_rev13.epub
These plugins are specially laid out zip archives that contain the python source code so that you can see and edit it as needed. A few people do use github repos for their plugins. You can search github to find most of them.