What is measured
The audit validates link rel=canonical, resolves relative values, and compares the result with the page’s final URL.
Technical access and indexing
Canonical URL
This check shows which page version the website nominates as primary among duplicate or alternate addresses.
Pass criterion
A unique page points to itself, while known duplicates consistently reference one accessible canonical version.
What to fix
Fix a missing, invalid or contradictory canonical and align it with redirects, the sitemap and internal links.
Automation limit
Canonical is a strong hint rather than an unconditional command. Conflicting signals can make a search engine select a different version.
Reference