Key takeaways
- A canonical tag names the preferred address when several addresses show the same content.
- Search engines treat it as a strong hint, not an order.
- The common errors are pointing to the wrong page and pointing every page to the home page.
A canonical tag is a line in a page's head that names the address you consider the main version of that page. When the same content can be reached at several addresses, it tells search engines which one to show and which to treat as copies. It is a hint that Google usually follows, not a command.
What it looks like
<link rel="canonical" href="https://example.com/shoes/running/" />
Put it in the head of every page that can be reached at more than one address. A page should normally point to itself when it is the main version.
When you need one
- The same product is reachable with and without tracking parameters.
- A category can be sorted or filtered into many addresses.
- The site is served on both
wwwand the bare domain, or on http and https. - You syndicate or republish content and want the original credited.
A worked example
| Address | Canonical points to | Result |
|---|---|---|
/shoes/running/ | /shoes/running/ | The main version |
/shoes/running/?sort=price | /shoes/running/ | A copy, folded into the main page |
/shoes/running/?utm_source=mail | /shoes/running/ | A copy, folded into the main page |
Mistakes that cause trouble
- Pointing every page's canonical at the home page, which tells search engines to ignore them all.
- Pointing at an address that redirects, returns an error or is blocked.
- Pointing two pages at each other.
- Using a relative address that resolves to the wrong place.
- Combining a canonical with a noindex tag on the same page, which sends mixed signals.
- Letting a template output the same canonical on pages with different content.
How to check
Fetch a handful of addresses from each template, look at the canonical on each, and confirm that it points to a page that returns a normal response, shows the same content and points to itself. Then compare with what Google chose: the page indexing report shows when your choice was overruled.
The wider picture
Canonicals are one part of a clean site structure, alongside redirects, sitemaps and internal links. They are covered in our technical SEO checklist and fixed in our technical SEO work.