What is a canonical tag?
A canonical tag (rel="canonical") is an HTML element that tells search engines which version of a URL is the "authoritative" or "preferred" version. It is used to prevent duplicate content from diluting ranking signals across multiple similar URLs.
When to use canonical tags
Common scenarios requiring canonicalization: paginated content (page 1 vs page 2), parameter-based URLs (product pages with sort/filter parameters), HTTP vs HTTPS versions, www vs non-www, and content syndicated to multiple domains.
Canonical tags are a hint, not a directive. Google may override them if it determines the tag is incorrect or if another signal (like a redirect) contradicts it. Canonical errors are one of the most common findings in technical SEO audits.
Example
Example
Your product page is accessible at /products/widget/, /products/widget?color=red, and /products/widget?ref=homepage. A canonical pointing all variants to /products/widget/ consolidates their signals.
Frequently asked questions
Is a canonical tag a directive Google must follow?
No, it is a hint. Google overrides canonicals that conflict with stronger signals like redirects, internal links, or sitemap entries. Consistency across all signals is what makes canonicalization stick.
Should a page have a self-referencing canonical?
Yes. A canonical pointing to the page’s own clean URL protects against parameter variants and scraped copies claiming the original, and it is the convention crawlers expect.