A canonical tag is a line of HTML that tells search engines which URL is the main version of a page when similar content exists at several addresses. It is the standard technical SEO fix for duplicates caused by tracking parameters, sorting options, print versions and copied content.
<link rel="canonical" href="https://www.example.com/red-shoes/" />
It sits in the head of the page. Google treats it as a strong hint, not a command, and weighs it alongside redirects, internal links and sitemaps, as explained in its guide to consolidating duplicate URLs.
Why canonicals matter
One product can easily live at five URLs: with and without a trailing slash, with a colour parameter, with a tracking code and in a category path. Without guidance Google picks one itself, splits link signals between them and may show the wrong one. A canonical consolidates everything onto your chosen URL and is the main defence against duplicate content.
When to use a canonical tag
- Self-referencing: every indexable page should point to itself. This protects against parameters added by others.
- Parameter URLs: /shoes/?sort=price should point to /shoes/.
- Product variants: colour or size URLs with near-identical content point to the main product.
- Syndicated content: if a partner republishes your article, ask them to add a cross-domain canonical to your original.
Canonical vs 301 redirect vs noindex
Use a 301 redirect when the old URL should no longer be visited at all. Use a canonical when both URLs need to work for users but only one should rank. Use a noindex tag when a page should not appear in search but has no better equivalent.
How to set canonicals in WordPress
Rank Math and Yoast add self-referencing canonicals automatically. To point a page elsewhere, open the plugin’s Advanced tab on that page and enter the canonical URL.
Common mistakes
- Pointing every page on the site to the homepage.
- Canonicalising paginated pages (page 2, 3) to page 1, which can hide the products on later pages.
- Pointing to a URL that redirects, is noindexed or returns a 404.
- Using relative URLs that break on staging or alternative domains.
- Having two canonical tags on one page, often from a theme and a plugin.
- Canonical in the sitemap URL not matching the canonical on the page.
How to check canonicals
Use URL Inspection in Google Search Console. It shows the user-declared canonical and the one Google selected. If they differ, Google disagrees with you, usually because internal links, sitemaps or content point the other way.
Frequently asked questions
Does a canonical pass link equity?
Google consolidates signals to the canonical URL, so links to duplicates generally benefit the main page.
Can I canonicalise to another domain?
Yes. Cross-domain canonicals are supported and common for syndication.
Related terms
See XML sitemap, hreflang and the SEO encyclopedia.
Mr. SEO
Mr. SEO is the webmaster at SEO TT - SEO tips and tricks, a publication about all things SEO related.