Canonical points to external URL

This means that the URL in question has a canonical element pointing at an external URL (a URL on a different domain or subdomain). This is known as a 'cross-domain canonical'.

Why is this important?

Cross-domain canonicals are often used when a publisher syndicates content from another source - they can set a cross-domain canonical to indicate that the original source URL is the canonical version.

If Page A is canonicalized to Page B, it is explicitly marking Page B as it's canonical. This acts as a strong signal to search engines that these two pages should be considered duplicate, and that Page B should be prioritised.

If a URL contains a cross-domain canonical, this indicates to search engines that they should consolidate link signals to the canonical URL (i.e. if Page A has some external links pointing at it, Page B will get the value for these links).

What does the Hint check?

This Hint will trigger for any internal URL which contains a canonical link element (either in the HTML or in the HTTP header) which specifies an external URL as the canonical URL. An external URL is defined as being on a different subdomain.

Examples that trigger this Hint:

Consider the URL: https://example.com/page-a

The Hint would trigger for this URL if it had any of the following;

Canonical link in the <head> to a URL on a different root domain:

<link rel="canonical" href="https://another-website.com/page-b" />

Canonical link in the <head> to a URL on a different subdomain.

<link rel="canonical" href="https://blog.example.com/page-b" />

HTTP Header canonical link to a URL on a different root domain.

HTTP/... 200 OK

...
Link: <https://another-website.com/page-a>; rel="canonical"

HTTP Header canonical link to a URL on a different subdomain.

HTTP/... 200 OK

...
Link: <https://blog.example.com/page-a>; rel="canonical"

Why is this Hint marked 'Advisory'?

In Sitebulb, this Hint is Advisory, as it does not represent a clear issue. Canonicals implemented in this manner are usually deliberate, so they are flagged in Sitebulb in order to draw your attention to the URLs that have cross-domain canonicls, so you can double check that they have been implemented correctly.

While Sitebulb can check if a canonical tag is valid, it has no way of knowing for sure that Page B should be the canonical URL for Page A.

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