What Is a Canonical Tag?
A canonical tag (also called rel=canonical) is an HTML element that tells search engines which version of a URL is the "master" copy when the same or very similar content exists at multiple URLs. It is placed in the <head> section of the page.
<link rel="canonical" href="https://www.example.com/page">
When You Need Canonical Tags
- URL parameters —
/shoes?color=redand/shoes?sort=priceshow the same core content - WWW vs non-WWW —
www.site.com/pageandsite.com/page - HTTP vs HTTPS — same page accessible on both protocols
- Trailing slashes —
/pageand/page/ - Syndicated content — your article republished on another site
- Mobile URLs —
m.site.comandwww.site.com
How Canonical Tags Affect SEO
Without canonical tags, search engines may index multiple versions of the same page. This splits your link equity across duplicate URLs, dilutes your ranking signals, and wastes crawl budget. Canonical tags consolidate all signals to a single URL.
Canonical Tag vs 301 Redirect
| Method | Use When | User Sees |
|---|---|---|
| Canonical tag | Both URLs need to stay accessible | Can visit both URLs |
| 301 redirect | Old URL should no longer be used | Automatically sent to new URL |
Check if your pages have canonical tags with the canonical URL checker.
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Last updated: March 2026