CANONICAL TAGSOne URL for every page
SELLWRIGHTMost marketing sites serve the same page at more than one address without anyone planning it. An ad click adds ?gclid= to the URL, a blog filter adds ?sort=, and a forgotten demo copy turns up in search. A canonical tag tells Google which of those URLs you want shown. Set up properly, it removes a lot of confusion. It also fixes less than many people expect.
What does a canonical tag do?
A canonical tag names your preferred URL for a set of duplicate or very similar pages. Google calls the process of picking that representative URL canonicalization, and your tag is one of its inputs. It is a single link element in the page <head>:
<link rel="canonical" href="https://www.example.com/services/web-design/" />When Google accepts it, signals such as links to the different versions are consolidated into one URL, your reports stop splitting the same page across several addresses, and Googlebot spends less time on copies. Google crawls the canonical page most regularly and its duplicates less often.
When do you need one?
You need one wherever the same content can load at more than one URL, which on most sites means every indexable page. The usual sources of duplicates on a marketing site:
- Tracking parameters, such as
?gclid=from Google Ads or the campaign tags on email links. - Sorting and filtering on blog, resource or product listings.
- Protocol variants: the
http://andhttps://versions of the same page. - Regional pages with essentially the same content in the same language.
- A demo or staging copy of the site left open to crawlers.
If you use a CMS, it may set the canonical for you or offer a setting for it. Your job is then to check what it actually outputs.
How do you set it up correctly?
Follow Google's rules and keep every signal pointing the same way:
- Use the full absolute URL, including
https://. Google supports relative paths but advises against them, because they cause trouble if a test copy of the site is ever crawled. - Place the tag in the
<head>. Google only accepts it there, so the head must be valid HTML. - Add a self-referencing canonical on the preferred page itself, as Google recommends, as well as on the duplicates that point to it.
- Link internally to the canonical URL, never to a parameter or duplicate version.
- Don't name one URL in the tag and a different one in your sitemap.
- Put the canonical in the HTML source. If JavaScript renders the page, make sure it doesn't change the tag afterwards.
- For PDFs and other files without a
<head>, send the canonical as an HTTPLinkheader.
Why does Google sometimes ignore it?
Because a canonical is a hint, not a rule. Google says so directly, and it may choose a different page for reasons such as the quality of the content or technical signals. Redirects and canonical tags are strong signals, sitemap inclusion is a weak one, and they become more effective when they agree. When your tag names one URL, your navigation links to another and your sitemap lists a third, Google has to decide for itself.
What can't a canonical tag fix?
A canonical can't make different pages the same, and it can't hide a page from search. These are the common misuses:
- Near-identical location or service pages. If ten city pages share the same copy, Google may cluster them and show one. The fix is content that is genuinely different; Google says pages split out faster when the difference is clear and significant.
- Paginated archives. Pointing page 2 and page 3 of a blog archive at page 1 is wrong; Google advises giving each page in a sequence its own canonical.
- Blocking duplicates in robots.txt. Google can't read a tag on a page it doesn't crawl, and may still index the blocked URL without its content.
- Using
noindexto choose between duplicates. Google doesn't recommend it, because it removes that page from Search entirely.
How do you check which URL Google chose?
Use the URL Inspection tool in Search Console. It shows the user-declared canonical, which is your tag, next to the Google-selected canonical. That choice only appears in the indexed result; the live test can't predict it. In the Page indexing report, "Alternate page with proper canonical tag" means a duplicate points correctly and needs no action, while "Duplicate, Google chose different canonical than user" means Google disagreed and your signals deserve a look.
Where to start
Open your five most visited pages, view the source and confirm each has one absolute, self-referencing canonical in the head. Then add ?gclid=test to one of those URLs and check that the canonical still points to the clean address. For a site-wide check, our SEO and AI search service audits canonicals alongside the rest of your technical SEO, or start with a website review.
FAQ
Frequently asked questions
Is a missing canonical tag a problem?
Usually not a serious one. Google says none of the canonical methods are required, and it will choose the best version itself if you don't specify one. We still add a self-referencing canonical to every indexable page, because it costs one line and settles the question before parameters or filters create copies.
Does duplicate content get a site penalised?
No. Google says some duplicate content on a site is normal and isn't a violation of its spam policies. The cost is practical rather than a penalty: signals such as links get split across versions, the wrong URL can appear in results, and crawling time goes on copies instead of new pages.
Should sites that republish our articles use a canonical tag?
Google doesn't recommend relying on the canonical element for syndicated copies, because partner pages are often very different from the original. Its advice is for partners to block indexing of the republished version, so your original is the one that appears in Search. Agree this with partners before the article goes out.
How long does Google take to pick up a canonical fix?
It depends on when Google recrawls the pages. Even after duplicate content is fixed, Google says pages can stay in a duplicate cluster for up to two weeks. You can ask for a re-evaluation with Request Indexing in the URL Inspection tool, but it has quotas, so save it for your most important URLs.
Will Google choose HTTPS over HTTP on its own?
By default, yes: Google prefers HTTPS pages over equivalent HTTP pages as canonical. Conflicting signals can override that, such as an invalid certificate, an HTTPS page that redirects through HTTP, or a canonical tag pointing at the HTTP version. Keep your sitemaps and canonical tags on HTTPS URLs only.
Can a plugin or theme set the wrong canonical?
Yes. Google lists incorrect canonical elements from content management systems and plugins among the common causes of unexpected canonicals. Check what the page actually outputs with view source or your browser's developer tools, and check again after theme or plugin updates, not only at launch.
