SEO Glossary
What is Canonical Tag?
A canonical tag (rel="canonical") is an HTML element that tells search engines which version of a page is the "main" or "preferred" one when similar or duplicate versions exist. It consolidates link equity and prevents duplicate content issues.
Canonical tags are essential for any site with duplicate or similar content across multiple URLs.
1
Why canonical tags are needed
Duplicate content is more common than you think. The same page might be accessible via:
• https://site.com/page and https://www.site.com/page
• https://site.com/page and https://site.com/page?ref=email
• Product pages in multiple categories
• HTTP and HTTPS versions
• With and without trailing slashes
Without canonicals, search engines might:
• Split ranking signals across duplicate URLs
• Index the "wrong" version
• Waste crawl budget on duplicates
2
How to implement
Add in the <head> section of the duplicate page:
<link rel="canonical" href="https://yoursite.com/preferred-page" />
The canonical URL should be the absolute, full URL of the preferred version.
Self-referencing canonicals (pointing to the page itself) are also recommended as a best practice on every page.
3
Canonical tags vs 301 redirects
Use 301 redirects when:
• You've permanently moved content to a new URL
• Users should only access one version
Use canonical tags when:
• Both URLs need to remain accessible to users
• You have URL parameter variations
• Content is very similar but not identical
• You syndicate content across domains
Canonical tags are hints - Google may choose to ignore them. 301 redirects are directives that are always followed.
4
Common canonical mistakes
• Pointing to non-existent URLs
• Canonicalizing paginated pages to page 1
• Conflicting canonicals and noindex tags
• Using relative URLs instead of absolute
• Canonical chains (A → B → C instead of A → C)
• Canonicalizing to a different domain unintentionally
• Setting canonicals via both HTTP header and HTML tag with different values
FAQ
Frequently asked questions
Should every page have a canonical tag?
Yes, self-referencing canonical tags on every page is a best practice.
Can I canonical to a different domain?
Yes, cross-domain canonicals work for syndicated content, but use them carefully.
Related Terms
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