What is a canonical tag?

A canonical tag is an HTML element ( ) placed in the section of a page. It tells search engines which URL should be considered the authoritative version of the content. This is essential for handling duplicate content, URL parameters, and HTTP/HTTPS or www/non-www variations.

Why can't the tool fetch the URL directly?

Browser security (CORS) prevents JavaScript from fetching arbitrary URLs. This tool works by parsing HTML source code you paste in, which is more reliable and works offline. For automated URL-based checking, use our full website scanner.

What does self-referencing canonical mean?

A self-referencing canonical points back to the same page (the URL in the canonical tag matches the current page URL). This is the correct setup for the primary version of a page. It is considered an SEO best practice to include self-referencing canonicals on all pages.

When should the canonical point to a different URL?

When you have duplicate or very similar content on multiple URLs -- for example, the same product on /products/shoe and /sale/shoe -- the less important version should canonical to the primary version. Also use it for paginated content, URL parameter variations, and syndicated content.

Is it bad to have multiple canonical tags?

Yes. Having multiple canonical tags with different URLs confuses search engines. They may ignore the canonical entirely or pick one unpredictably. Always ensure only one canonical tag exists per page.

Should canonical URLs be absolute or relative?

Always use absolute URLs (https://example.com/page) in canonical tags. While some search engines can resolve relative URLs, using absolute URLs avoids ambiguity and is recommended by Google.

Does this tool check HTTP header canonicals?

This version checks HTML source code only. Canonical tags can also be set via HTTP Link headers (for non-HTML resources like PDFs). If you need to check HTTP headers, use the browser Network tab or curl.

How often should I check canonical tags?

Check after any major site change -- CMS migration, URL structure changes, new templates, or plugin updates. Also check periodically (monthly) as part of your SEO audit routine. Our full scanner checks canonical tags automatically across your entire site.

SEO

Canonical Tag Checker

Check canonical tags in HTML source code. Detect missing, self-referencing, or conflicting canonical URLs with detailed warnings.

100% free
No sign-up
No limits
Instant results

Page URL (optional -- for self-reference check)

HTML source code

What this tool does

Parses <link rel="canonical"> from HTML source
Detects missing canonical tags
Checks self-referencing vs cross-domain canonicals
Warns about multiple conflicting canonical tags
Validates URL format (absolute, no hash, no whitespace)
100% client-side -- your HTML is never sent anywhere

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The short version

What is Canonical Tag Checker?

A canonical tag (rel=canonical) tells search engines which version of a page is the preferred one when duplicate or similar content exists at multiple URLs.

This tool parses HTML source code to find canonical tags, check if they are self-referencing, detect conflicts from multiple canonical declarations, and validate URL format. Proper canonical implementation is critical for preventing duplicate content penalties in search rankings.

Step by step

How to use Canonical Tag Checker

1
Get the HTML source
Visit the page you want to check. Right-click anywhere on the page and select "View Page Source" (or press Ctrl+U). Copy the entire HTML source code.
2
Enter the page URL
Optionally enter the current page URL in the URL field. This allows the tool to check whether the canonical is self-referencing (points to itself) or points to a different page.
3
Paste the HTML
Paste the copied HTML source code into the text area. The tool will search for <link rel="canonical"> tags in the markup.
4
Review results
Click Check Canonical. The tool shows the canonical URL found, whether it is self-referencing, any warnings (missing, multiple, malformed), and actionable recommendations.

What's inside

Everything this tool
does for you

Finds <link rel="canonical"> tags in HTML source code
Detects missing canonical tags with setup instructions
Checks self-referencing vs cross-page canonical status
Warns about multiple conflicting canonical declarations
Validates URL format (absolute URL, no hash fragments)
Detects query parameters and whitespace issues
Color-coded results: green (good), yellow (warning), red (error)
100% client-side -- your HTML source stays in your browser

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Questions

Frequently asked questions

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