Canonical Tag
A hint naming the preferred URL among duplicates, so ranking signals consolidate on one page.
A canonical tag is the link rel="canonical" element that names the preferred URL for a page. When the same content is reachable at several addresses — with tracking parameters, with and without a trailing slash — the tag tells search engines which one to index and which to treat as a duplicate, consolidating the signals onto a single URL.
Definition
The canonical tag — <link rel="canonical" href="..."> — tells search engines which URL is the preferred version of a page when several URLs serve substantially the same content.
It is a hint, not a directive. Google weighs it alongside internal links, sitemap membership, redirects and hreflang, and will overrule a canonical it considers wrong. This is why Search Console distinguishes the "user-declared canonical" from the "Google-selected canonical" — when those disagree, the page you wanted indexed is not the page that is.
Self-referencing canonicals on every page are standard practice: they settle tracking parameters, trailing slashes and protocol variants without you enumerating them.
Across every site SlapMyWeb has audited, 60.2% declare a canonical URL — which leaves 39.8% with no canonical tag.
Measured from SlapMyWeb audits of live public URLs. The full aggregate is published as a CC-BY-4.0 dataset.
Why It Matters
Duplicate URLs split the signals that would otherwise accumulate on a single page — links, engagement, crawl attention. Consolidating them is often the cheapest ranking improvement available, because it adds no content and no links; it just stops the site from competing with itself.
Example
A shop reachable at /shoes, /shoes?sort=price and /shoes?utm_source=news is three URLs and one page. A self-referencing canonical to https://example.com/shoes on all three tells Google to treat them as one. Note that the canonical must be absolute and must point at a URL that returns 200 — pointing it at a redirect or a 404 makes it noise.
Related Terms
Related Tools
Know the term.
Check your own site.
A free audit tells you whether this is currently costing you score points — and exactly what to change.
Run a free audit