Cross-Domain Canonical Example
I declared my true residence to be the Island of Cheese, and it was perfectly true, for I had eaten my way to the front door.
The short answer
- What it is
- A cross domain canonical is a canonical tag that points to a URL on a different registrable domain. It tells search engines that the main version of the page is on that other site.
- Why it matters
- Done on purpose, it helps merge copies across your own sites. Done by mistake, it asks search engines to drop your page in favor of someone else's.
- How a crawler should report it
- A crawler should show a cross-domain canonical warning with the page URL, the target URL, and the target's registrable domain. The row should also count as canonicalized and non-indexable.
- Live examples
/lab/canonical-cross-domain/(positive), on the second shelf
Naming a page on another website as the original
A cross domain canonical is a canonical tag whose target sits on another registrable domain. It might look like <link rel="canonical" href="https://example.com/"> on a page at some other site. A valid use is a business with several sites that publishes the same article on each one. Google has supported this kind of tag since 2009. Subdomains of one site do not count, since they share a registrable domain.
Mistakes are more common than you might think. A site may be cloned from another one and keep the old domain in its templates. A staging domain can leak into production through a setting. A developer may hard-code a domain. Hacked sites can have tags added that point to a spammer's domain. In each case, you are asking search engines to credit another site for your own page.
Browsers ignore the tag, and visitors stay on your page. Search engines treat it as a hint, so they may or may not obey. If they do, your URL can leave the results, and the target shows in its place. For syndicated content, Google now says that the tag is not the best tool, since partner pages often differ. It suggests that partners block their copies with noindex instead.
To detect it, compare the registrable domain of each canonical target to that of the page. Use the public suffix list, so that example.co.uk is handled right. Review each result by hand. To fix a mistake, change the tag to your own URL, and correct the setting that caused it. If the tag is intended, confirm that the target is live, that it can be indexed, and that its content matches your page.