A canonical tag indicates the preferred version of a page when the same or similar content exists at multiple URLs. It consolidates search signals onto a single address and prevents duplicate content issues. The tag is placed in the page's head section.
A product page reachable through different filter parameters in the URL points, via canonical, back to the clean main address.
In-depth guide
A canonical tag tells the search engine which version of a page is the original when the same or near-identical content exists at multiple addresses. It solves one of the most common technical SEO problems, duplicate content, where Google would otherwise have to guess which URL should rank.
The tag sits in the page’s <head> and points to the preferred address:
<link rel="canonical" href="https://example.com/product" />A page that points to itself is called a self-referencing canonical, and this is completely normal and recommended. Problems typically arise when filters, sorting or tracking parameters create many variants of the same page:
https://example.com/shoes
https://example.com/shoes?colour=black
https://example.com/shoes?sort=price&page=2All three should point to the clean version with a canonical tag, so the authority is gathered in one place.
canonical.In Google Search Console you can also use URL Inspection to see which canonical Google itself has chosen. It can differ from yours, and if so, there’s something to fix.
A canonical tag is a signal, not an order, so Google can choose to ignore it if it points somewhere that doesn’t make sense. The classic mistakes are pointing every page to the homepage, pointing to a page blocked in robots.txt, or forgetting the tag altogether on an ecommerce catalogue with thousands of filter variants. Set up correctly, canonical is one of the most effective tools in technical SEO.
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