Free crawlability check
Canonical Tag Checker
The canonical link tells search engines which url is the real one when several show the same content. Check that it exists, that it is absolute and that it points at a working page.
Check a canonical
Enter the address of a page. The checker reads its canonical and tests the host variants.
Why use the Canonical Checker
Present and absolute
A relative canonical works but invites mistakes. The checker reports the exact value it found.
Target tested
The canonical url is requested. One that redirects or fails sends search engines in a circle.
Host variants
www, bare and trailing slash variants are tested so duplicates are caught at the host level too.
Self reference confirmed
A page that points at itself is the safe default, and the checker confirms it.
When to use the Canonical Checker
Duplicate pages
Check that filtered, sorted and tracked urls all point at the clean version.
Syndicated content
Confirm that republished articles point back to the original.
Template bugs
Catch a template that gives every page the home page as its canonical.
HTTP and HTTPS mixes
Spot canonicals that still point at the http version of a page.
Migrations
Make sure new pages do not point at the old domain.
Pagination
Check that page two of a list is not canonicalised to page one by mistake.
Understanding Canonical
What a canonical does
rel=canonical is a hint that says which url represents a page when the same content is available at several addresses. Search engines usually follow it and consolidate links and signals on that url.
It is a hint, not a directive. If the canonical points at a very different page, or at a redirect or an error, search engines ignore it and choose for themselves.
Rules that keep canonicals working
- 1Absolute urls. Use the full https address including the host.
- 2One per page. Several canonical links cancel each other out.
- 3Indexable target. The target must answer with 200 and must not carry noindex.
- 4Consistent signals. Internal links, the sitemap and the canonical should all name the same url.
Canonical or redirect
If people never need the duplicate url, a permanent redirect is stronger and simpler. Use a canonical when the duplicate has to stay reachable, for example a filtered list or a print version.
Privacy, safety and limits
The check runs on Aback servers as AbackAuditBot. It sends ordinary GET and HEAD requests, never a cookie, a password or a form, and it never changes anything on the site.
The result is stored as a report that anyone with its link can open, and it is deleted after 30 days. Do not check addresses that carry secrets in the path or the query string.
Related tools and guides
Frequently asked questions
Should every page have a canonical?
Yes. A self referencing canonical on every page protects against tracking parameters and host variants creating duplicates.
Can the canonical point to another domain?
Yes, for syndicated content. The other page must carry substantially the same content.
Does Google always follow the canonical?
No. It is one signal among several. Redirects, internal links and the sitemap also count, and Google may pick a different url if they disagree.
What about the canonical in the HTTP header?
A Link header with rel=canonical works too, mostly for PDFs and other files. Do not send conflicting values in the header and the HTML.
Is a canonical to the home page bad?
Only on pages that are not the home page. It tells search engines the page is a duplicate of the home page, so it can drop out of the index.
Do AI assistants use canonical links?
AI search crawlers that build an index tend to treat canonicals like search engines do. It helps them cite the right url.
Why do host variants matter here?
If both www and bare hosts serve pages, every page has a duplicate. A canonical helps, but a redirect from one host to the other removes the duplicate altogether.