- Adds markdown syntax highlighting to GitHub textareas

- Lists every open PR/issue tab and any drafts

- (Optional, unimplemented) autosaves your comment drafts so you don’t lose work

I made it because I was impressed by https://overtype.dev/ (a markdown textarea syntax highlighter) which went big on here on HN a few weeks ago, and it seemed like a perfect fit for a GitHub browser extension. Keeping up with changes on upstream GitHub would normally be a pain, but with with Playwright and Claude Code it seemed possible for it to be nearly automatic, which has turned out to be mostly true!

This was the first time where I built a tool, gave the tool to AI, and then AI used the tool to make the thing I hoped it would be able to make. I'm pretty sold on the general technique...

GitHub repo (Apache2-licensed, open source): https://github.com/diffplug/gitcasso

Video walkthrough (2 mins of the tool, 12 mins of its development tooling): https://www.youtube.com/watch?v=wm7fVg4DWqk

And a text writeup with timestamps to the video walkthrough https://nedshed.dev/p/meet-gitcasso