Canonical URL
The preferred URL for a page when multiple URLs contain similar content.
What is Canonical URL?
A canonical URL tells search engines which version of a page is the "master" copy when the same or similar content exists at multiple URLs. This is specified using the rel="canonical" link element in the HTML head.
Canonicalization solves duplicate content issues caused by URL parameters, HTTP vs HTTPS, www vs non-www, trailing slashes, and syndicated content. Without proper canonicals, search engines may index the wrong version or split ranking signals between duplicates.
Why Canonical URL matters
Duplicate content confuses search engines and dilutes ranking power. When the same content exists at multiple URLs, Google must choose which to index and rank. Proper canonicalization ensures your preferred URL gets all the ranking signals and prevents duplicate content penalties.
How to implement
Add rel="canonical" to every page pointing to itself
Use absolute URLs (https://example.com/page)
Ensure canonicals are consistent across the site
Point pagination to the main page or use self-referencing
Handle URL parameters with canonical tags
Audit canonicals regularly with SEO tools
Code example
<link rel="canonical" href="https://example.com/page/" />Common mistakes to avoid
- Pointing canonical to a 404 or redirected page
- Using relative URLs instead of absolute
- Conflicting canonical and redirect signals
- Forgetting canonicals on paginated content
Examples
Product page with filters: /products/shoes?color=red canonicalizes to /products/shoes
HTTP page canonicalizes to HTTPS version
Syndicated content on partner site canonicalizes to original
Frequently asked questions
Yes, every indexable page should have a self-referencing canonical tag. This prevents issues if the page is accessed via different URLs.
Yes, cross-domain canonicals work for syndicated content. The canonical URL should be the original source of the content.