Canonical tag
Definition
A canonical tag is an HTML element used to tell search engines which version of a webpage should be treated as the primary source. It is placed in the head section of a page and helps consolidate duplicate or similar pages so that ranking signals are directed to the correct URL.
For example, an online store might have the same product listed under several categories, generating duplicate URLs. By applying a canonical tag that points to the main version, the store prevents confusion and ensures the preferred page is shown in search results.
Advanced
Canonical tags are part of technical SEO and play a key role in handling duplicate content. They are especially useful for e-commerce sites, dynamic URLs, and sites with parameters for filters or tracking. While the canonical tag is a strong signal, search engines may override it if other signals conflict.
Advanced implementation includes self-referencing canonicals, managing cross-domain canonicalization for syndicated content, and using them with hreflang attributes in multilingual sites. Tools like Google Search Console and crawling software can verify whether canonical signals are being interpreted correctly. Mistakes such as pointing canonicals to non-indexable URLs or chains of canonicals can lead to ranking issues.
Why it matters
Use cases
Metrics
Issues
Example
A fashion retailer has the same product accessible under /dresses/red-dress and /sale/red-dress. To prevent duplication, a canonical tag is placed on both pages pointing to /dresses/red-dress. As a result, search engines index the preferred page, consolidating authority and improving ranking stability.