Narzędzie do sprawdzania tagu kanonicznego SEOptimer szuka obecności tagu kanonicznego w HTML Twojej strony. Google zaleca posiadanie tego tagu na każdej stronie.
The Canonical Tag is a HTML Tag that tells Search Engines the primary URL of a page. URLs can have multiple versions due to things like parameters being passed or www and non-www versions, resulting in potential duplicate content. Google recommends all pages specify a Canonical for this reason.
You may need to determine what the primary preferred version of the page is. Often the CMS may manage this, or provide the ability to specify it.