What Is Canonical URL?
A canonical URL is the preferred version of a web page that search engines should index when multiple URLs serve the same or very similar content. It's specified using a <link rel='canonical'> tag in the page's HTML head.
Why It Matters
Duplicate content is a common SEO problem. The same page might be accessible at multiple URLs:
http://example.com/pagehttps://example.com/pagehttps://www.example.com/pagehttps://example.com/page/https://example.com/page?utm_source=twitter
Search engines see each of these as a potentially different page. Without guidance, they have to guess which one to index — and they might choose the wrong one, or split ranking signals across all variants.
Canonical vs Redirect
Canonicals and 301 redirects solve different problems:
Use a canonical when multiple URLs need to remain accessible (e.g., pages with tracking parameters) but you want search engines to consolidate ranking on one version.
Use a 301 redirect when you want to send both users AND search engines to a single URL. The old URL becomes inaccessible — anyone visiting it is automatically forwarded.
If you have a choice, a 301 is stronger. Canonicals are hints that search engines may ignore. Redirects are directives that must be followed.
How It Works
Add a <link> tag to the HTML <head>:
<link rel="canonical" href="https://www.example.com/preferred-page">Search engines use this to consolidate ranking signals from all duplicate URLs onto the canonical URL. The non-canonical URLs may still show up in browser results, but Google will increasingly favor the canonical.
Common Mistakes
Setting a canonical that redirects. If the canonical URL itself returns a 301, search engines receive conflicting signals. Make sure the canonical URL returns a 200 status.
Self-referencing canonicals missing. Every page should include a self-referencing canonical tag pointing to its own URL. This prevents issues with query strings and URL variations.
Canonical across domains. You can set a canonical pointing to a different domain. This tells search engines the other domain has the preferred content — useful for syndicated content but surprising if done accidentally.
How Domain Forward Handles This
Domain Forward complements canonical URLs. When you permanently forward a domain with a 301 redirect, search engines are redirected to your canonical domain. This is stronger than a <link rel="canonical"> tag because it ensures both users and search engines reach your preferred domain.
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