Canonical URL
A canonical URL is the address you designate as the main version of a page when the same or almost the same content appears at several addresses. You indicate it with a canonical tag in the code.
- 3 min read
What is a canonical URL?
A canonical URL is the preferred version of a page. You indicate it with a short line in the head of the page, the canonical tag. That is a link element with rel=”canonical” and the address of the main version in it. With it you tell search engines: if you come across this content at several addresses, this is the address that counts.
That is necessary because the same page is often reachable via different addresses without you realising it. With and without www, with and without a slash at the end, with parameters behind it such as ?utm_source=facebook, or via a sorting option. To you it is one page. To a search engine they are different addresses with the same content.
A canonical is a strong hint, not a command. Google usually follows the indication, but may deviate if other signals say something different.
Why it matters for your business
Duplicate content means Google has to choose which version to show. Sometimes it picks a different one than you would like, for example an address with a tracking parameter. Signals such as backlinks are also spread across several versions instead of being bundled on one page.
For a trade business with a straightforward website this may seem like a technical detail. But local pages are exactly where it goes wrong quickly. Location pages that look alike, a service page that also sits under a project category, or an old version of the site that is still reachable. A wrong canonical can even cause an important page not to appear in Google at all.
How it works
Every page gets a canonical tag that points to itself, the so-called self-referencing canonical. If a copy or variant exists, it points to the original. Search engines then bundle the signals on the designated address and show that in the search results.
Other signals also help make the choice clear. A permanent redirect from the non-www version to the www version, or the other way round. Internal links that always point to the main address. And a sitemap that only contains the canonical addresses.
An example. Say a solar panel company runs ads with UTM parameters, so that every click on an ad lands on an address like /zonnepanelen/?utm_source=google. The site is also reachable via http and https, and with and without www. In theory there are therefore several versions of the same service page. Without a proper canonical, Google finds all those variants and has to choose for itself.
With the right settings, all variants point via the canonical tag to https://www. and the clean address /zonnepanelen/. Http and non-www are redirected. The internal links point to the clean address. That way everything counts towards one page.
Common mistakes
The most dangerous mistake is a canonical that points to the wrong page. That happens, for example, when a template sets the homepage as the canonical on every page. Google then sees all your service pages as copies of the homepage and leaves them out.
A second mistake is a canonical to an address that does not work, redirects or is set to noindex. Google then gets conflicting signals.
Also often seen: a staging or test environment that is public and has the same content as the real site, without a canonical or noindex. Your test site then competes with your real site.
Finally, some people think a canonical solves near-identical pages. Twenty location pages with the same text and a different place name cannot be fixed with canonicals. Each of those pages needs its own content, with real information about the work in that place, or they need to be merged.
How to approach it
First check whether every important page has a canonical that points to itself. In WordPress, an SEO plugin usually handles that automatically. Do check that it is right, especially on pages built with a page builder. Open the source code of a page and search for “canonical”, and you will see straight away which address is in there.
Choose one main version of your domain, with or without www and always with https, and redirect the other versions with a permanent redirect. Make sure your internal links and your sitemap only use the main address.
Use Google Search Console to see which canonical Google chooses itself. In the indexing report you can see pages where Google has chosen a different version from yours. That is a signal to investigate. More about how Google reads your site can be found at crawling and indexing.
When in doubt, this belongs in a technical check of your site. We include it in technical SEO.
Frequently asked questions
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What is the difference between a canonical and a redirect?
A redirect sends visitors and search engines straight to another address. A canonical leaves the page reachable, but tells search engines which version is the main one. Use a redirect when a page can go, and a canonical when variants need to stay.
Does every page need a canonical?
It is sensible to give every indexable page a canonical that points to itself. That avoids confusion with variants that have parameters or different spellings. Many SEO plugins handle this automatically.
Can a canonical error get my page removed from Google?
Yes. If a canonical points to another page, Google sees the page as a copy and usually only shows the designated version. A template error that sets the homepage as the canonical everywhere can keep your service pages out of the search results.
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