Quick answer
Add a canonical link when a page needs to communicate its preferred URL among duplicates or variants. For a genuinely unique page, a self-referencing canonical is often a clear policy, but do not add canonicals mechanically to every response.
What the issue means
A canonical is a <link rel="canonical" href="…"> declaration. It is a hint about the preferred representative, not a redirect and not an access-control mechanism. It should point to a URL that is accessible and appropriate for indexing.
Why it matters for SEO
Clear canonical signals can help consolidate URL variants and reduce ambiguity. Missing canonical metadata does not automatically mean a page is broken; page purpose, internal links, redirects, sitemap entries, and other signals matter.
How NOTABIS detects it
The missing-canonical rule reports when no canonical is measured on a crawled page. It does not decide the preferred URL for you. Check the page’s status, indexability, URL parameters, and site policy before choosing a value.
How to check it yourself
View the delivered HTML and search for canonical links. Confirm there is one intended value, that it uses the correct scheme and host, and that the target returns the expected response.
How to fix it
Set the canonical in the server-side template or CMS using a stable absolute URL. Normalise only the variants your site treats as equivalent, then update internal links and sitemaps where needed. Re-crawl the page and inspect the emitted value.
When it may be intentional
Private, non-indexable, redirect, error, or non-HTML responses may not need a canonical. A page with no meaningful duplicate or preferred representative may warrant a policy review rather than an automatic tag.
Related issues
Review canonical presence, multiple canonicals, off-origin canonicals, and canonical/noindex conflicts.
Run a NOTABIS audit
NOTABIS measures the delivered canonical and provides page-level evidence for missing values.