Canonical URL
A tag that tells search engines which address is the ‘official’ one when the same page can be reached by several URLs.
In plain English
The same page can often be opened at slightly different addresses (with or without www, with tracking parameters, http vs https). To a search engine those can look like separate, duplicate pages — splitting your ranking strength between them.
A canonical tag is you pointing and saying “this one is the real address; credit it.” It consolidates all that strength onto a single URL.
How to fix / set it up
- Decide your preferred URL format (usually https + one of www/non-www).
- Add a self-referencing canonical link to every page's head.
- Point true duplicates (parameter URLs, print pages) at the main version.
The technical detail
Add <link rel="canonical" href="https://example.com/page"> in the page's <head>, pointing at the preferred absolute URL. Each page should canonicalise to itself unless it's a genuine duplicate.
Mismatched or missing canonicals cause duplicate-content dilution and unpredictable indexing.
FAQ
Does every page need a canonical?
It's good practice for every page to declare a self-referencing canonical, so duplicates via parameters or protocols don't split signals.
Is a canonical a redirect?
No — it's a hint, not a redirect. The duplicate URL still loads; search engines just credit the canonical one.