Canonical Tag
The canonical tag (<link rel="canonical">) tells search engines which version of a URL is the "master" copy when duplicate or similar content exists across multiple URLs.
Reviewed by Alexander Yarovenko · Updated: 2026-09-18
What is a Canonical Tag?
The canonical tag is an HTML element placed in the <head> of a page that signals to search engines which URL is the preferred (canonical) version of a page. When duplicate or near-duplicate content exists at multiple URLs, the canonical tag tells Google which version should be indexed and credited with any ranking authority.
Canonical Tag Syntax
<!-- In the <head> of the duplicate page -->
<link rel="canonical" href="https://example.com/preferred-page/">When to Use Canonical Tags
- HTTP and HTTPS versions of the same page
- www and non-www versions
- Trailing slash vs no trailing slash URLs
- Faceted navigation / filter pages (e.g.
/shoes?colour=red&size=42) - Paginated pages (canonical to page 1 or component pages)
- Print-friendly versions of pages
- Product pages syndicated to partner sites
- UTM-tracked URLs (add self-referencing canonical to the original URL)
Self-Referencing Canonicals
Every page should have a canonical tag pointing to itself — even if it has no duplicates. This is called a self-referencing canonical and it confirms to Google that this URL is the preferred version, protecting it from being accidentally treated as a duplicate.
Canonical vs 301 Redirect
| Canonical tag | 301 redirect | |
|---|---|---|
| Removes duplicate URL | ❌ Both URLs stay accessible | ✅ Old URL redirects away |
| Preserves link equity | ✅ Yes (hint, not guarantee) | ✅ Yes (stronger signal) |
| Use when | You want both URLs to remain accessible | You want to permanently remove the old URL |
How to use this concept in SEO
Canonical is a consolidation hint, not a command. The strongest setup is consistent: the preferred URL returns 200, self-canonicalizes, appears in the sitemap, and receives the internal links.
Audit checklist
- Confirm that the implementation matches the page purpose and the user task.
- Check the HTTP response, rendered HTML, canonical, robots rules, and internal links together.
- Use Search Console and analytics to verify the result instead of relying on one crawler signal.
- Test a representative URL on mobile and desktop after deployment.
- Document the expected outcome so regressions can be detected in the next audit.
Practical example
Filtered URLs such as ?sort=price can canonicalize to the clean category URL when their main content is substantially the same.
How to validate the result
Record the current crawl, indexation, performance, and traffic state before changing anything. Recheck the affected template and a representative URL after deployment, then monitor Search Console over the following crawl cycle. A technical change is complete only when the live response and Google’s observed state agree.