Tool for detecting and removing duplicates? [Available in 8.10.18]

I've already managed to clean up many of my duplications - but there's still more to go through.

Although only slightly on-topic, it would be nice to have a URL-checker built-in to find entries in 1Password for sites that no longer [seem to] exist - kind of like what watchtower does for identifying sites that have known password breaches. It would allow you to find, verify, and remove entries for old/dead sites and sites that no longer use accounts (I've come across several such sites where I used to have a login and where there no longer is a place to log in on them anymore). I'm spending a lot of time just trying to verify that these sites still exist to know how much effort to put into dealing with their duplications or weakness of passwords, etc.