Awesome! So the agent has access to the DOM/JS running in the browser?

That’s one of my biggest headaches writing user scripts currently: I write the script in an IDE with Claude then copy it to the browser / manually test it in the browser, then copy the results back to Claude or tell it what went wrong.

Looking forward to trying this.

to my knowledge all the major userscript extensions, at least allow watching for file changes so you don't have to copy it manually, so you can just refresh the page to test

Yup, full access to DOM! Still needs a lot of optimizations, but the trick is that the agent reads the DOM as file, so it can grep parts of it naturally.