http://www.aiai.ed.ac.uk/~jeff/lisp/cl-pitfalls is now gone; it looks like ~jeff is gone.

wayback machine to the rescue! https://web.archive.org/web/20171007090745/http://www.aiai.ed.ac.uk/~jeff/lisp/cl-pitfalls

is this issue still looking for someone to help?

if you find an automated tool for that, that would be very nice ! (there must be many out there)

Hope it's ok i'm upping here instead of creating a new issue.
Just pulled a request on an updated link to the CL standard, the cvberry website appears to have become a link farm. More details in the request.
It appears link rot is a serious concern, that particular web squatting link is full of aggressive JS.

Not sure if an automated link-checking tool would be possible, as the squatter in my example just sent a redirect as opposed to "not found".
I'm going to slowly review other external links in the cookbook. The more people do this, the better.