What Is a Canonical Tag in SEO? How and When to Use It
How the canonical tag tells Google which version of a page to index, with examples and the mistakes to avoid.
The same page can often be reached at several addresses: with and without www, with tracking parameters, with a trailing slash or without, through a category path or directly. To you it is one page. To a search engine, each address could be a separate, duplicate page. The canonical tag is how you say which address is the real one.
What the canonical tag does
A canonical tag is a line in the page's head section that names the preferred URL for that content. When Google finds several URLs with the same or very similar content, it uses the canonical tag โ together with other signals like redirects, internal links and sitemaps โ to choose one URL to index and show in results. Signals such as links pointing to the duplicates are then consolidated on that one URL.
It is a strong hint, not a command. If your other signals contradict the canonical tag, Google may choose a different URL.
When you need a canonical tag
- Tracking and session parameters โ
?utm_source=,?ref=,?sessionid=. - Sorted and filtered listings that show the same products in a different order.
- Products in several categories with a different URL for each path.
- Printer-friendly or AMP versions of the same article.
- Syndicated content republished on another site with your permission.
Self-referencing canonicals: a good default
Every indexable page should have a canonical tag pointing to its own clean URL. This protects you automatically when someone links to a version with parameters. It also tells search engines that you have made a deliberate choice about the preferred URL. Most modern CMSs and SEO plugins add this for you; check that they do.
Canonical tag or 301 redirect?
- Use a 301 redirect when the old URL should no longer be visited at all โ the page moved, merged or changed address.
- Use a canonical tag when both versions must stay accessible to visitors, such as filtered views or tracking links, but only one should appear in search.
Test redirects with the redirect checker to make sure they go straight to the final page.
Mistakes that cause problems
- Every page canonicalised to the homepage. A common theme or plugin bug that tells Google only your homepage matters.
- Canonical pointing to a redirected, noindexed or 404 URL. The target must be a live, indexable page.
- Relative URLs or the wrong protocol. Use the full address, such as
https://www.example.com/page. - Conflicting signals. The canonical says one URL, the sitemap and internal links use another.
- Two canonical tags on one page, often added by a theme and a plugin together. Google may ignore both.
How to add and check canonical tags
The free meta tag generator creates the canonical tag along with your title and description. To check many pages at once โ including whether each canonical points to itself or elsewhere โ use the bulk indexability checker. If Search Console shows "Duplicate without user-selected canonical", canonical tags are usually the fix. For wider context, see why pages end up crawled but not indexed.
Related guides
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Frequently asked questions
Does every page need a canonical tag?
It is best practice for every indexable page to have a self-referencing canonical tag.
Can a canonical tag point to another website?
Yes, for syndicated content you republish with permission, the copy can point to the original article.
Will a canonical tag remove a page from Google?
It asks Google to index the canonical version instead. The duplicate usually drops out of results, but it stays accessible to visitors.
How do I see which canonical Google chose?
Use URL Inspection in Search Console. It shows the user-declared canonical and the Google-selected canonical.