Canonical URL
What is a canonical URL?
A canonical URL is the address you tell search engines to treat as the main version of a page reachable at several addresses. It is set with a canonical tag in the page’s code, so copies created by filters and parameters stop competing with the original and links to them count for one page. Google treats it as a strong signal, not an order, so redirects, internal links and the sitemap should name the same address.
Example
A shoe shop has 400 models. Each one opens from three places: its own category, the Sale section, and a colour filter that adds a parameter to the address. That turns 400 pages into 1,200 addresses (400 × 3) with identical content, and the search engine decides for itself which one to show. It often picks the awkward one: the sale is over, and the result still points to the Sale address.
The fix is a canonical tag on all three versions pointing to one address, say /ankle-boots-model-x/. Shoppers keep their filters, and the search engine keeps a single page that every link to the product works for.
Why it matters for a business
Duplicate addresses are not penalised, but they split what the page has earned. A link from a partner or a newspaper lands on one version while another one ranks, and neither is as strong as one page holding everything. Search Console has a separate status for pages where Google chose a different canonical from the one you declared — the first sign that the site is sending mixed signals.
On a site in two languages, each language version should point to itself. If the English page names the Bulgarian one as canonical, Google may treat it as a copy and leave it out of the results.
What to ask
- Does every page carry a canonical pointing to itself, written in full: https, the right domain, the same trailing slash every time?
- What happens to the addresses created by filters, sorting and campaign parameters such as utm?
- When do you use a canonical, and when a 301 redirect? A redirect sends people and crawlers to the new address; a canonical keeps the page open to visitors and only tells the search engine which version to keep.
- Do the canonicals match the sitemap and the internal links?
We check canonicals in the technical part of SEO and AI search, starting with the addresses Google has already chosen.