Duplicate URLs appear constantly: tracking parameters, HTTP vs HTTPS, trailing slashes, printer-friendly versions, faceted e-commerce filters. Left unmanaged, they split ranking signals across near-identical pages and waste crawl budget. A canonical tag points all those variants at a single authoritative URL.
It is a hint, not a directive — Google can ignore a canonical if it conflicts with other signals like internal links, sitemaps or 301 redirects. So canonicals must be consistent with the rest of your setup. A self-referencing canonical on every page is a safe default that removes ambiguity.
Common mistakes include canonicalising to the wrong page, mixing canonical with noindex, or pointing paginated pages at page one. When you genuinely want to move a URL for good, a 301 redirect is stronger than a canonical; the canonical is for cases where both URLs must stay live.
FAQ
Frequently asked questions
A 301 physically sends users and bots to another URL and is a strong signal to drop the old one. A canonical keeps both URLs accessible but tells search engines which to index. Use 301 to consolidate permanently, canonical when both must stay live.
