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

I created a Perl script to process the exported CSV from 1Password to create a new CSV file sorted by duplicate count (in descending order so that the ones with duplicates appear above the ones without). You could then open this resultant CSV file in Numbers (or Excel, or similar) and then manually work your way down the list - searching for the given Title or Url and then examining (!) each entry to choose one to keep and then archive or delete the rest.
(! examine carefully because my code only looks at the first four fields: Title, Url, Username, and Password, it does NOT look at OTPAuth, Favorite, Archived, Tags, or Notes - so you might need to do some manual merging before archiving/deleting the redundant entries).

Save the script to your Downloads folder (e.g., ~/Downloads/1pecsv.pl), Export your 1Password data as CSV (e.g., ~/Downloads/1PasswordExport-1234858.csv) and you can then run it from the command line.

 cd ~/Downloads
 perl ./1pecsv.pl ./1PasswordExport-1234858.csv ./1pe.csv

In the end, you'd see:

 RESULTS IN: ./1pe.csv

If you then go to ~/Downloads in your Finder, you should be able to click on that file (1pe.csv), and it will open in whatever application you have associated with CSV files. From there, it's a manual back-and-forth between that file and 1Password.

Theoretically, one could modify the script to generate a unique listing, and then you could archive/delete everything you have in 1Password and Import the resultant CSV file - but I'm not willing to claim that would be safe.

If you don't have Perl installed on your computer you might have to download and install it - for that, I suggest you go through Google or whatever your web-browser-search-engine-of-choice is.