Canonical URL
An HTML element specifying the preferred version of a webpage when duplicate or similar content exists at multiple URLs.
Definition
A canonical URL (specified via the rel="canonical" tag) tells search engines which version of a page is the "master" copy when the same or similar content exists at multiple URLs. This prevents duplicate content issues that can dilute ranking signals and confuse search engines.
Common scenarios requiring canonicalization include HTTP vs. HTTPS versions, www vs. non-www, URL parameters for tracking or filtering, mobile versions, and syndicated content. Proper canonical implementation ensures all ranking signals consolidate to your preferred URL.
Why It Matters
Without proper canonicalization, search engines might split ranking signals across multiple URLs, weakening each version's ability to rank. In severe cases, the wrong version might rank, or pages might be filtered as duplicates entirely.
Canonical tags are especially critical for e-commerce sites with faceted navigation, news sites syndicating content, and any site with tracking parameters appended to URLs.
Examples in Practice
An e-commerce site implements canonical tags on filtered product pages, consolidating signals to the main category page and improving rankings.
A publisher syndicates articles with canonical tags pointing to the original, preventing syndication partners from outranking them.
A marketing team adds canonical tags to campaign landing pages with UTM parameters, preventing parameter variations from creating duplicate content.