Canonical Tag Checker
Analyze your page's canonical tag implementation. Check for missing tags, duplicate canonicals, protocol issues, og:url consistency, and other common mistakes that cause duplicate content problems.
- Detects missing, duplicate, or malformed canonical tags
- Validates absolute URLs, HTTPS protocol, and proper placement
- Compares canonical URL against og:url for consistency
How to Use This Canonical Tag Checker
Check your canonical tag implementation in four simple steps.
Paste Your HTML Source
Copy the full HTML source of a page (view-source in your browser) and paste it into the text area. You can also paste a partial <head> section.
Run the Checker
Click the check button. The tool extracts canonical tags, og:url, and other meta tags, then runs multiple validation checks.
Review Each Check
Each check shows pass, warning, fail, or info status. Expand each result to see the detected values and recommended fixes.
Fix and Re-Test
Correct any issues in your HTML source, then paste the updated version to verify all canonical checks pass.
Paste Your HTML Source
Copy the full HTML source of a page (view-source in your browser) and paste it into the text area. You can also paste a partial <head> section.
Run the Checker
Click the check button. The tool extracts canonical tags, og:url, and other meta tags, then runs multiple validation checks.
Review Each Check
Each check shows pass, warning, fail, or info status. Expand each result to see the detected values and recommended fixes.
Fix and Re-Test
Correct any issues in your HTML source, then paste the updated version to verify all canonical checks pass.
Canonical Tags: The Complete Guide to Preventing Duplicate Content
The canonical tag is one of the most important yet frequently misimplemented elements in technical SEO. Introduced by Google, Microsoft, and Yahoo in 2009, the rel="canonical" link element solves a fundamental problem: the same content often lives at multiple URLs. Whether through URL parameters, session IDs, tracking codes, www vs. non-www variants, HTTP vs. HTTPS versions, or syndicated content, duplicate URLs dilute ranking signals and confuse search engines about which version to index.
The canonical tag addresses this by declaring a single, authoritative URL for each piece of content. When search engines encounter a canonical tag, they consolidate all ranking signals (links, engagement metrics, crawl data) from the duplicate URLs to the canonical version. This concentration of signals typically results in stronger rankings for the canonical URL compared to having those signals spread across multiple versions.
How Canonical Tags Work
A canonical tag is placed in the <head> section of an HTML document as a link element: <link rel="canonical" href="https://example.com/page">. When Googlebot or another crawler encounters this tag, it treats the specified URL as the preferred version and will consolidate indexing signals accordingly.
It is important to understand that the canonical tag is a hint, not a directive. Search engines will generally respect it, but they may override your canonical if they determine it is incorrect -- for example, if the canonical URL returns a 404 error, redirects elsewhere, or points to content that is substantially different from the current page. This is why proper implementation matters: search engines are more likely to follow your canonical if it is technically correct and logically consistent.
When to Use Canonical Tags
The most common use cases for canonical tags include:
URL parameter variations. E-commerce sites frequently generate URLs with sorting, filtering, and tracking parameters. A product page at /products/shoes might also be accessible at /products/shoes?sort=price, /products/shoes?color=red, and /products/shoes?utm_source=email. All variations should canonicalize to the clean URL without parameters.
Protocol and subdomain variants. If your site is accessible at both http:// and https://, or at both www and non-www, canonical tags prevent these from being indexed as separate pages. While 301 redirects are the preferred solution here, canonical tags serve as a backup signal.
Content syndication. When your content is republished on other websites, the republished version should include a canonical tag pointing back to the original URL on your domain. This ensures the original receives the ranking credit, not the syndicated copy.
Print and mobile versions. If your site serves separate print-friendly or mobile-specific URLs (rather than using responsive design), these alternative versions should canonicalize to the primary URL.
Common Canonical Tag Mistakes
Using relative URLs is one of the most frequent errors. A canonical tag with href="/page" instead of href="https://example.com/page" may be misinterpreted, especially when the page is accessed through different hostnames or CDN domains. Always use absolute URLs in canonical tags.
Multiple canonical tags on a single page create conflicting signals. This typically happens when a CMS plugin adds a canonical and the theme template also adds one. When search engines encounter multiple canonicals, they may ignore all of them and make their own determination -- which may not be what you intended.
Canonicalizing to a non-indexable page wastes the consolidation benefit. If your canonical URL returns a 404, is blocked by robots.txt, or has a noindex tag, the canonical signal is contradictory and search engines will likely ignore it.
Chain canonicals -- where page A canonicalizes to page B, which canonicalizes to page C -- reduce the effectiveness of the signal. Each hop introduces a chance that the signal will be lost or misinterpreted. Canonical tags should always point directly to the final, preferred URL.
Canonical Tags and Other Signals
The canonical tag does not work in isolation. Search engines evaluate it alongside other URL signals including 301 redirects, internal linking patterns, sitemap inclusion, hreflang tags, and the og:url meta property. When all these signals are consistent -- pointing to the same preferred URL -- search engines have high confidence in your intent. When they conflict, search engines must make a judgment call, and the outcome may not match your preference.
For this reason, a comprehensive approach to duplicate content involves aligning all URL signals. Your technical SEO strategy should ensure that canonical tags, redirects, sitemaps, internal links, and Open Graph tags all point consistently to the same preferred URLs. Our SEO audit service checks for canonical inconsistencies across your entire site and identifies every page where signals conflict.
Frequently Asked Questions
Everything you need to know about canonical tags and duplicate content prevention.
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