Canonical URL

The same page often exists at more than one address: with and without "www", with tracking parameters, sorted or filtered versions of a product list, or a print view. A search engine picks one of these as the canonical and folds the others into it, so signals such as links are not split across copies.

The rel="canonical" tag lets you suggest which URL that should be, but it is a signal, not a directive. Google weighs it alongside redirects, internal links, sitemaps and HTTPS, and may choose a different URL if your signals contradict each other.

How it works

You declare a canonical with a link element in the page's head (rel="canonical" pointing at the preferred URL) or in an HTTP header for files such as PDFs. Most pages should have a self-referencing canonical that points to their own clean address. Duplicates point to the main version.

Google's URL Inspection tool in Search Console shows both the canonical you declared and the one Google selected. When they differ, Google has found stronger signals elsewhere, such as internal links pointing to the other version. Pages with only small differences, such as a product in two sizes, are commonly treated as duplicates.

Canonicals only make sense between pages that really are duplicates or near-duplicates. If two pages have substantially different content, Google is likely to ignore a canonical between them, because the hint contradicts what it sees. Cross-domain canonicals are also supported, for example when the same content is deliberately published on two sites you own. Canonical URLs should be absolute, include the correct protocol and host, and point to a page that returns a normal success response.

Example

An online shop's product pages are reachable through several category paths and with colour and sort parameters, creating dozens of URLs per product. Each variant declares the clean product URL as canonical, internal links use only that URL and the sitemap lists only that URL. Search Console soon reports the clean URLs as the Google-selected canonicals.

To check its own pages, the shop pastes a product URL into URL Inspection and compares the "User-declared canonical" with the "Google-selected canonical". On a few products they differ, because an old category menu still links to the parameter versions. Updating that menu to link to the clean URLs brings the two into line. A site crawler can also list every page's declared canonical to spot mistakes in bulk.

Why it matters for your business

Canonicals prevent your own site from competing with itself and keep ranking signals focused on the address you want people to land on. Getting them wrong can quietly remove important pages from results, for example when every page canonicalises to the home page. For a small brochure site, correct defaults from the CMS are usually all that is needed. A quick check of a few page types in URL Inspection is usually enough to confirm the setup is correct.

Common mistakes

• Pointing every page's canonical at the home page, which tells search engines the other pages are duplicates.
• Using a canonical when a 301 redirect is the right tool, such as after moving a page permanently.
• Declaring one canonical while internal links and the sitemap point at a different version.
• Combining a canonical with a noindex tag on the same page, which sends conflicting signals.

Questions people ask

Is a canonical tag a directive or a hint?

A hint. Google treats rel="canonical" as a strong signal, but it combines it with redirects, internal links, sitemaps and other clues, and may pick a different URL if they disagree. Redirects are a stronger signal. Keeping all signals consistent is the reliable way to get the canonical you want.

Should every page have a canonical tag?

It is good practice for each indexable page to have a self-referencing canonical pointing to its own clean URL. That protects against duplicates created by tracking parameters and other variations. Most modern CMS platforms and SEO plugins add this automatically, so check it is present and correct rather than writing it by hand.

What is the difference between a canonical and a 301 redirect?

A 301 redirect sends visitors and crawlers to another URL, so the old one is no longer viewable. A canonical leaves both URLs working for visitors and only suggests which one search engines should index. Use a redirect when a page has moved; use a canonical when duplicates must stay reachable.