Canonical URL
A canonical URL is the address you designate as the primary version of a page when the same content is reachable through several URLs. It is declared with `` in the <head>.
Duplicates appear from small things: www versus non-www, http versus https, trailing slashes, ?utm_source=... parameters, or filtered category pages. Without a canonical, search engines have to guess which one is primary.
How it works
When a crawler finds several URLs with similar content, the canonical tag signals: "use this URL as the reference". It is not a redirect; visitors can still open the other URLs. That is why canonical and redirect have different jobs.
| Situation | Correct action |
|---|---|
| One piece of content, several live URLs | Canonical to the primary URL |
| Old URL should no longer be used | 301 redirect to the new URL |
| Product page with filter parameters | Canonical to the unfiltered version |
| Paginated pages | Self-canonical per page, not to page 1 |
Practical rules
- Use an absolute URL (
https://example.com/page), not a relative path. - Each page should have one canonical; do not output two different tags.
- The primary page should be self-referencing — canonical to itself.
- Keep it consistent with the sitemap and internal links; do not canonical to a URL blocked by
robots.txtor returning 404. - In WordPress, many themes add a canonical automatically. Check the HTML output before adding another plugin.
What to watch for
Canonical is not a fix for every duplicate. If two pages are genuinely different and both important, do not force a canonical to one of them. If an old URL is no longer used, a redirect is stronger than a canonical. And if a canonical points to a noindex page, the signals conflict.
FAQ
What is the difference between canonical and redirect?
A redirect moves visitors to another URL. A canonical leaves the URL accessible but tells search engines which URL is primary.
Should every page have a canonical?
Preferably yes, at least self-referencing. It reduces crawler guesswork when parameters or URL variations exist.
Can a canonical point to another domain?
It can, but only when the content is intentionally published on that other domain. For a normal website, cross-domain canonicals risk moving signals to someone else.
Disclaimer: Hosting Wiki articles are prepared for educational and reference purposes. Hosting technology keeps evolving, so some technical details may change over time.