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Technical SEO

What is a canonical tag, and when should you use one?

A canonical tag tells search engines which URL is the main version of a page. When you need one, how to write it, and the mistakes that send signals elsewhere.

A canonical tag is a link element in a page's head that names the preferred URL for that content. It tells search engines which version to index when the same page is reachable at several addresses, such as with tracking parameters or with and without www. Every indexable page should point to its own clean URL.

Published · Last updated

By Michal Měřínský. Audit methodology.

What a canonical tag is

<link rel="canonical" href="https://example.com/pricing">

It says: whatever address you reached this page by, the main version lives here. Search engines use it, along with redirects, sitemaps and internal links, to decide which URL to show in results and where to consolidate ranking signals.

Why the same page has several URLs

  • Tracking and sorting parameters: ?utm_source=newsletter, ?sort=price.
  • Host and protocol variants: http and https, www and bare domain.
  • Trailing slashes and letter case.
  • The same product reachable through several category paths.
  • Syndicated or copied content on another site. Without a canonical, Google picks one itself. Often it picks well. Sometimes it picks a parameter URL you never wanted in results.

How to use it

  • Put a self-referencing canonical on every indexable page, with the full absolute URL.
  • On duplicates, point the canonical at the main version.
  • Keep it consistent with everything else: the canonical URL should be the one in your sitemap, in your internal links and the target of your redirects.
  • Use the exact host and protocol you serve, https and www or not, matching your redirects.

A canonical is a strong hint, not a command. If your links, sitemap and redirects point elsewhere, Google may ignore it.

Canonical, redirect or noindex?

  • Use a 301 redirect when the old URL should not be visited at all.
  • Use a canonical when both URLs must keep working, such as a filtered view people need.
  • Use noindex when a page should not appear in search at all. Do not combine noindex with a canonical pointing elsewhere: they contradict each other.

Common mistakes

  • Every page canonicalised to the homepage, often from a template default. Google may then ignore the tags, or treat inner pages as duplicates.
  • Canonicals pointing at a staging or preview domain after launch.
  • Relative URLs or the wrong protocol.
  • Canonicals added by JavaScript after load in single-page apps, which some crawlers never see.
  • Paginated pages all canonicalised to page one, which hides the content on later pages.

What a scan can and cannot tell you

WebAuditOS checks that each crawled page declares a canonical link in its served HTML, and warns when a canonical points to a different host, such as a preview domain. It also checks for long redirect chains and unreadable parameter-heavy URLs, which are where duplicates usually come from.

It does not check that the canonical target returns 200, that the two pages are really equivalent, or which canonical Google finally chose. Search Console's URL Inspection shows the Google-selected canonical.

A page whose canonical points at the homepage passes the presence check. Look at where your canonicals point, not only whether they exist.

Short answers

Does every page need a canonical tag? It is not required, but a self-referencing canonical on every indexable page prevents ambiguity.

Is a canonical the same as a redirect? No. A redirect moves visitors. A canonical only advises search engines.

Can a canonical point to another domain? Yes, for syndicated content you want credited to the original.

Why did Google choose a different canonical? Your other signals, such as links and sitemaps, disagree with the tag.

In the product

The checks this maps to

Every check named here runs on every scan, on every plan - what a plan changes is how many pages are crawled, how long the history is kept and what you can do with the result. These are the ids the findings carry, so you can match a line in a report to the explanation above.

Technical SEO

What is a 301 redirect, and when should you use it?

A 301 permanently moves a URL and carries its search signals to the new one. When to use 301, 302, 307 or 308, and how to avoid chains and redirect mistakes.

Technical SEO

Why a page is not in Google, in the order to check it

Robots rules, noindex, canonicals, status codes, redirect chains and JavaScript-only content - the technical reasons a page never gets indexed, worst first.