A duplicate page has exactly the same text as another page on the site, under a different address. Google then has to guess which one to show.
Duplicates split links and attention between two addresses. Google usually indexes one of them, and not always the one you want.
Snaglist makes a fingerprint of the readable text of every indexable page. Pages with the same fingerprint are listed together, with the other address and the number of copies.
Snaglist runs this check and 43 others on every page of your site, every week. 14 days free, no credit card needed.
Try free for 14 days