What is Canonical Tag

How it works

Common duplicate scenarios include tracking parameters, HTTP vs HTTPS, www vs non-www, trailing slashes, and print or paginated versions. Point each variant at the clean canonical URL so link equity accrues to a single page.

Common mistakes

Canonicalising every page to the homepage, using relative URLs, or setting a canonical that is itself noindexed or blocked. A page should almost always be self-referential unless it is a genuine duplicate.

• Always use absolute URLs
• Do not canonicalise to a redirected or 404 URL
• Keep canonical and hreflang consistent

Why it matters

The canonical tag is how you tell Google which URL is the "master" version when the same or very similar content is reachable at multiple addresses — a near-universal situation caused by tracking parameters, faceted filters, HTTP/HTTPS, trailing slashes, and print or AMP variants. Without it, duplicate URLs split ranking signals between themselves, so no single version accumulates the authority it should, and Google may pick a canonical you did not intend. Used correctly, it consolidates all that duplicate equity onto the one URL you want ranking.

• Consolidates ranking signals from duplicate URLs onto one master version
• Prevents Google picking the "wrong" URL as canonical
• Essential wherever parameters, filters or protocol variants create duplicates

It is a hint, not a directive

A crucial nuance: rel=canonical is a strong hint, not a command. Google can and does override it if your other signals disagree — for example, if the "canonical" you declare is noindexed, redirects elsewhere, or is clearly not the best version. This is why canonical signals must be consistent: the declared canonical should be self-referencing where appropriate, indexable, linked internally, and match the version in your sitemap and hreflang. When signals conflict, Google trusts the weight of evidence over the tag alone.

• Google treats it as a hint and can override contradictory signals
• The canonical URL should be indexable, self-referencing and internally linked
• Keep canonical, sitemap, internal links and hreflang all pointing the same way

Worked example

An e-commerce category page is reachable at four URLs: the clean path, a `?sort=price` variant, a `?page=1` variant and a session-tracking variant. Left alone, links and ranking signals scatter across all four and none ranks as well as it should. The fix is a self-referencing canonical on the clean URL and a canonical on each variant pointing back to it, so Google consolidates all their equity onto the one master page. Crucially, the team also checks that the canonical target is indexable, internally linked and the version in the sitemap — because if those signals disagreed (say the sitemap listed the `?sort=price` version) Google might override the tag. After the change, the four URLs behave as one page in the index, and its rankings improve because it now receives the combined authority rather than a quarter of it.