Canonical URL signals
Short answer
Redirects, rel="canonical" and sitemap inclusion all tell Google which duplicate URL you prefer. Google treats them as signals and picks the canonical itself. Redirects and rel="canonical" are both strong signals, with redirects listed first; sitemaps are weak.
Methods
Section titled “Methods”| Method | Strength | Notes |
|---|---|---|
| 301 / 308 redirect | Strong | Use when the duplicate should no longer be visited. |
<link rel="canonical"> in HTML | Strong | Absolute URL in <head>. |
Link: <…>; rel="canonical" header | Strong | Works for non-HTML files such as PDFs. |
| Inclusion in a sitemap | Weak | Lists preferred URLs; easy to scale but weak. |
Rules of thumb
Section titled “Rules of thumb”- Each indexable page should declare a self-referencing canonical.
- Don’t point a canonical at a URL that is redirected,
noindex, or blocked by robots.txt. - Don’t use
robots.txtfor canonicalization (robots.txt controls crawling only). - For language versions, use hreflang, not a canonical pointing across languages. Each translation canonicalizes to itself.