Most site owners and marketers are aware that posting duplicate content is frowned upon by Google and will eventually negatively impact the site’s rankings. The problem here is that many post duplicate content unintentionally. Most will be completely oblivious to this issue until after the damage has already been done.
These duplications can occur for a number of reasons including URL parameters, CMS templates, and secure HTTPS pages. There are a myriad of tools that can be used to detect these carbon copy ranking killers. Screaming Frog, Link Sleuth, and the Moz Crawl Test are all fantastic options for obtaining this information. Once the duplicates have been uncovered, owners must then tell search engines to not index certain pages through either Noindex, Nofollow, or rel=canonical tags.