Canonical tags explained: stop duplicate pages splitting your rankings
A canonical tag tells search engines which address is the main one for a page. Here is when you need it, how to set it up and the mistakes that cause trouble.
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Put this into practice
Why do duplicate addresses happen?
The same page can often be reached at several addresses: with and without www, with a trailing slash, with tracking parameters on the end, or through filters and sorting on a shop page. Search engines see these as separate addresses with the same content, and have to decide which one to show.
What does a canonical tag do?
A canonical tag is a line in the page's head that names the preferred address. It is a strong hint, not a command, so a search engine may still choose differently if other signals disagree.
What should you set it to?
- On most pages, the page's own full address. This is called a self-referencing canonical and is a safe default
- On a true duplicate, the address of the main version
- Always a full address starting with https://, never a relative one
What mistakes cause problems?
- More than one canonical tag on a page, especially if they disagree
- A canonical that points to a different page by accident, so the page you want ranked tells search engines to ignore it
- A canonical on http when the page is on https
- Combining a canonical to another page with noindex, which sends mixed signals
- Tags added only by JavaScript, which some crawlers do not run
Frequently asked questions
Do I need canonical tags if I have redirects?
Redirects send people and bots to one address. Canonical tags cover addresses that must stay reachable, such as parameter versions. They work together.
Can a canonical point to another website?
Yes, and it is used when content is syndicated. Do it on purpose only, because it asks search engines to rank the other site's page.