📘 This article explains the importance of evaluating canonical tags for your website health.
Overview
A canonical tag indicates a page's content is not the primary version and points to the page with the main version (i.e., the canonical). It is a signal to advise search engines to present the canonical version in their search result pages, not the alternate version.
Evaluating Canonicalization Quality
Search engine bots can ignore a canonical tag because it is only an indication, not a directive. There are many reasons why bots ignore canonical tags, most commonly because poor implementation sends confusing signals, such as:
The canonical tag points to the wrong page, for example, a rich content page pointing to the homepage as its canonical.
Canonicalizing two pages to each other.
Canonical tag pointing to a page that is blocked by robots.txt.
Canonical tag pointing to a page that is set to “noindex”.
Canonical tag pointing to a page that 301s to the original page with the canonical tag.
The canonical tag points to a page in another language.
Internal linking contradicts the canonical tag: the canonical tag says the main version is a page that receives far fewer internal links than the non-canonical version. See how to check canonical tags and internal linking consistency and where non-canonical pages are linked from.
The canonical page is much slower.
There are many untrusted canonicals on the website, which indicates others cannot be trusted.
In addition to these quality issues, bots may ignore canonical tags for the following reasons:
User visits to the non-canonical version from all traffic sources are significantly more than visits to the canonical version, or the non-canonical has a higher click rate in search results.
The canonical page is not user-friendly on a mobile device.
Search engines may prefer a non-canonical page with a very precise query (i.e., long tail) if the specific expression it contains is not found in the canonical version.
Search engines may prefer a non-canonical version because the page has been updated and crawled recently, though it does not possess reliable information about the canonical page.
See also: