I use bookmarklets for a number of simple things.

My most used is to copy text where the formatting has been stripped, the bookmarklet prepends formatting instructions, and then I paste the whole thing into claude which sorts the formatting.

Me thinks I've underestimated what can be done with these.

Absolutely. If your account has access to the data, you can basically rewrite a website using a bookmarklet.

I wanted a friends feed in eBird (its social model is inscrutable) and ask Claude to make a bookmarklet that showed the most recent lists of my friends sorted chronologically. One shot and done.

Our internal corporate CRM is siloed data queries spread across overlapping views. I have a bookmarklet overlay my own interface on top and fetch data using the existing session token. (which is transparent/automatic - your browser just hangs on to the session cookies for the fetch calls)

Bookmarklets were definitely more powerful than I anticipated, but they’re tricky to version and upgrade. I’ve deployed a bookmarklet for non-technical users to some success, but I’d generally lean towards browser extensions for anything that needs to be maintained and distributed long-term.