The canonical URL is used to tell the engines what is the official URL of a page; This is useful in some cases to resolve duplicate content issues. But beware: misused, canonical URL can hurt your SEO!
Why is it necessary to monitor the canonical URL?
Since the time I do audits (2003!), I have encountered many kinds of errors with the canonical URL. I will summarize them here, which will save you from doing them too ...
Maybe you do not realize the large number of instances where a site contains errors at the canonical URL (which is not necessarily indicated via a URL, by the way).
13 Errors to Avoid with Canonical URL:
- The same URL is indicated as canonical for a very large number of pages on the site (yet having different contents)
- Several canonical URLs are indicated in string (A indicates B, which indicates C, etc.)
- A indicates B as canonical, but B redirects to A
- No canonical URL is specified for a page that is called with different URL parameters (eg utm_source and utm_medium, or "sort", "orderby", etc.)
- No canonical URL is specified on a non-responsive mobile site (for example, with m.example.com)
- A indicates B as the canonical URL, but B is in error 404 or forbids crawl (disallow in robots.txt) or indexing (meta robots noindex)
- The actual URL and the canonical URL indicated differ by a slash at the end (present or absent)
- The canonical URL is indicated in relative and not in absolute (begins with http), which is not a problem in itself, but sometimes the reconstructed URL is different or wrong
- The actual URL uses one or more uppercase letters but not the canonical URL (or vice versa)
- The actual URL uses URL rewriting but not the canonical URL (or the reverse)
- The canonical URL always corresponds to the URL consulted, without verification, whatever is added in the URL
- A indicates B as canonical, and B indicates A as canonical
- In case of pagination, on each URL (page 2, page 3, page 4 ...) one finds as canonical URL that of page 1
It does not look like anything, but by force it can really hurt your SEO, not only on Google for that matter.
Both check and correct if necessary! And do you know of other errors with the canonical URL?
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