What is a canonical tag?

A link element in the page head that tells search engines which URL is the preferred version when several URLs show the same or very similar content.

Is a canonical a directive?

It is a strong hint, not a command. Conflicting signals — redirects, noindex, internal links to another version — can cause it to be ignored.

Should every page have one?

A self-referencing canonical on each indexable page is good practice because it guards against parameter and tracking-URL duplicates.

Canonical tag checker

Enter a URL to read its canonical tag, compare it with the HTTP Link header and robots directives, and test the canonical target.

How to use the canonical tag checker

Enter the page URL.
Select Check canonical.
Review the declared canonical and each finding beneath it.
If the canonical points elsewhere, confirm that is intentional.

Examples

Self-referencing

https://example.com/guide/ declares <link rel="canonical" href="https://example.com/guide/">. This is the normal, healthy state for an indexable page.

A conflict

A page is noindex and also canonicalises to another URL. The two instructions contradict each other; pick one.

Understanding the results

Self-referencing: The page names itself as the preferred URL.
Points elsewhere: The page asks for another URL to be indexed instead. Correct for duplicates, a problem if unintended.
Target redirects or errors: The canonical URL does not resolve with a 200, so the hint is likely to be ignored.
Multiple tags: More than one canonical on the page. Search engines may disregard all of them.

Frequently asked questions

What is a canonical tag?: A link element in the page head that tells search engines which URL is the preferred version when several URLs show the same or very similar content.
Is a canonical a directive?: It is a strong hint, not a command. Conflicting signals — redirects, noindex, internal links to another version — can cause it to be ignored.
Should every page have one?: A self-referencing canonical on each indexable page is good practice because it guards against parameter and tracking-URL duplicates.