How to use the Canonical Tag Checker
Canonical bugs are silent — the page renders fine but Google indexes the wrong URL. The checker fetches the page, extracts the canonical, follows any redirects, and tells you whether the chain resolves correctly.
Enter the URL
Paste any URL on your site. The checker uses Googlebot's user agent so what it sees matches what Google sees.
Review the canonical declaration
Three places a canonical can live: <link rel="canonical"> in the head, Link: ... HTTP header, or implicit (Google picks one). The checker reports which path is in use.
Check the canonical chain
If the canonical points to a redirected URL, the checker follows the chain and shows every hop. Chains over 3 redirects often get ignored by Google entirely.
Confirm self-reference or cross-reference
Self-referencing canonicals (URL → same URL) are best practice. Cross-references (URL → different URL) need a clear reason — duplicate content, syndication, parameter consolidation.
Why canonical bugs are the most expensive technical SEO mistake
A wrong canonical can deindex your highest-ranking pages overnight without any visible symptom on the site itself. Auditing canonicals every few months catches drift before it costs traffic.
What can go wrong
- All pages canonical to homepage — entire site deindexes except the home.
- Canonical points to a 404 — Google ignores the tag and picks its own canonical.
- Canonical points to a 301 → 301 → 200 chain — chains over 3 redirects often get dropped.
- Mixed http/https canonicals — splits ranking signals between two indexed URLs.
- Trailing slash inconsistency — /page and /page/ canonical to each other in a loop.
What "correct" looks like
- Self-referencing canonical on every indexable page.
- Direct, single-hop canonical (no chains).
- Same protocol (https) and trailing slash convention as the rest of the site.
- Canonical URL returns HTTP 200, not a redirect or 404.
- On AMP/PDF/mobile alternates: canonical points to the desktop HTML version.
Frequently asked questions
How do I check the canonical tag of a URL?
Fetch the page and look for <link rel="canonical"> in the <head>. You can also check the HTTP response headers for a Link: <url>; rel="canonical" header. Use a tool like this checker, or curl: curl -s URL | grep canonical.
What if the canonical points to a different URL?
That's a cross-domain or cross-page canonical. It's valid when the target is the "master" version (e.g., a product page reachable via multiple categories canonicals to its primary URL). It's a bug when the target is unrelated or accidental.
Is it bad to have no canonical tag?
Not catastrophic, but suboptimal. Without an explicit canonical, Google picks one itself based on internal links, sitemap presence, and content similarity. Google's pick is usually right but not always — a self-referencing canonical removes the guesswork.
Can canonical tags cause deindexation?
Yes. The most dangerous pattern: all pages canonical to the homepage. Google will treat every page as a duplicate of the home and deindex them. Almost every massive deindexation incident on a high-traffic site traces back to a bad canonical template change.
Should canonical and og:url match?
Yes — both should point to the same canonical URL. A mismatch can cause Facebook to index a different URL than Google, fragmenting your social signals.
What Are Canonical Tags?
A canonical tag (also known as rel="canonical") is an HTML element that tells search engines which version of a URL is the "master" copy. It helps prevent duplicate content issues by consolidating ranking signals to a single preferred URL.
The canonical tag lives in the <head> section of a page and looks like this:
<link rel="canonical" href="https://example.com/preferred-page" />
Self-Referencing vs. Cross-Domain Canonicals
Self-referencing canonical: The canonical URL matches the page's own URL. This is the most common and recommended setup. It confirms to search engines that the current page is the preferred version.
Cross-domain canonical: The canonical URL points to a different page or domain. This is used when content is intentionally duplicated across domains or when you want to consolidate similar pages into one. For example, if you syndicate an article on Medium, the Medium version should have a canonical tag pointing back to your original article.
Common Canonical Tag Mistakes
- Missing canonical tag: Without a canonical tag, search engines must guess which version of a page to index. Always include a self-referencing canonical at minimum.
- Canonical pointing to a 404 page: If the canonical URL returns a 404 error, search engines may ignore it entirely, leading to indexing confusion.
- Multiple canonical tags: Having more than one canonical tag on a page sends conflicting signals. Search engines may ignore both.
- Canonical URL with different protocol: Pointing an HTTPS page's canonical to an HTTP version (or vice versa) creates a mismatch that can confuse crawlers.
- Relative URLs in canonical tags: While browsers can resolve relative URLs, it is best practice to use absolute URLs in canonical tags to avoid ambiguity.
- Canonical on paginated pages: Each page in a paginated series should have a self-referencing canonical, not all pointing to page 1.
How to Implement Canonical Tags
Add the canonical tag inside the <head> section of your HTML. Most CMS platforms (WordPress, Shopify, Squarespace) include canonical tags automatically, but you should verify they are set correctly.
- WordPress: Plugins like Yoast SEO and Rank Math automatically add canonical tags. You can override them per page in the post editor.
- Shopify: Canonical tags are added automatically to all pages by the theme.
- Custom HTML: Add
<link rel="canonical" href="https://yoursite.com/page" />in your<head>tag. - HTTP Header: For non-HTML resources (PDFs, etc.), you can set a canonical via the
LinkHTTP header:Link: <https://example.com/page>; rel="canonical"