What is a canonical tag?

A canonical tag ( ) tells search engines which URL is the definitive version of a page. When multiple URLs serve the same or similar content, the canonical tag prevents duplicate content issues and consolidates PageRank to the preferred URL.

What happens if a page has no canonical tag?

Search engines will attempt to determine the canonical URL themselves, which may not always match your preferred URL. This can split ranking signals across multiple URL variants and lead to unpredictable indexing.

Why should canonical URL and og:url match?

While og:url and canonical serve different purposes (social sharing vs SEO), having them differ can cause confusion and inconsistent signals. Best practice is to keep them identical so that both search engines and social platforms reference the same URL.

What are hreflang tags?

Hreflang tags tell search engines which language/region version of a page to serve to users in different locations. For example, a site with English and French versions uses hreflang to ensure French-speaking users see the French version in search results.

What does the robots meta tag do?

The tag controls whether search engines index the page and follow its links. Common values include 'index, follow' (default), 'noindex' (don't add to search index), 'nofollow' (don't follow links), and combinations thereof.

Can I check a URL directly?

Yes, if the target site allows cross-origin requests (CORS-permissive). Many sites restrict this for security reasons. If the URL fetch fails, you can view the page source manually (Ctrl+U in most browsers) and paste it into the HTML tab.

Does this tool support dynamic pages rendered with JavaScript?

No: this tool parses the raw HTML response, not the JavaScript-rendered DOM. For JS-rendered pages, you would need to copy the rendered source from browser DevTools (Elements panel → right-click → Inspect, then copy outer HTML).

Yes, completely free with no account required and no usage limits.

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Canonical Tag Checker

Inspect canonical tags, hreflang, robots meta, og:url, and more from HTML or a live URL.

HTML Source

Canonical tag checker: inspect canonical URLs, hreflang, robots, and OG tags for free

The canonical tag is one of the most important and most commonly misconfigured technical SEO elements. A missing, incorrect, or conflicting canonical can cause pages to compete against each other in search results, dilute link equity, and lead to the wrong URL appearing in Google's index. This tool gives you a complete picture of all canonical-related tags in one place.

Paste any HTML source and instantly see: whether a canonical tag exists, its exact URL, whether it conflicts with the og:url, all hreflang alternate tags, the robots directive, and the page title and meta description. Conflicts and missing tags are flagged with clear warnings so you can prioritise fixes. Copy the correctly formatted canonical tag HTML with one click.

Step-by-step guide

1
Paste HTML or fetch a URL
Paste the full page source (the <head> section is sufficient) or enter a URL for CORS-permissive sites to auto-fetch.
2
Review critical alerts
Missing canonical tags and URL conflicts are highlighted at the top as errors or warnings so the most important issues are immediately visible.
3
Check all findings
A full list of findings covers: canonical URL, title, meta description, robots directive, hreflang entries, og:url, og:title, and RSS feed link.
4
Copy the canonical tag
If a canonical tag is found, use the Copy Tag HTML button to copy the correctly formatted <link> element ready to paste into your HTML.
5
Inspect raw extracted tags
Expand the Raw Extracted Tags section to see all detected head tags formatted as clean HTML.

Frequently Asked Questions

What is a canonical tag?: A canonical tag (<link rel="canonical" href="...">) tells search engines which URL is the definitive version of a page. When multiple URLs serve the same or similar content, the canonical tag prevents duplicate content issues and consolidates PageRank to the preferred URL.
What happens if a page has no canonical tag?: Search engines will attempt to determine the canonical URL themselves, which may not always match your preferred URL. This can split ranking signals across multiple URL variants and lead to unpredictable indexing.
Why should canonical URL and og:url match?: While og:url and canonical serve different purposes (social sharing vs SEO), having them differ can cause confusion and inconsistent signals. Best practice is to keep them identical so that both search engines and social platforms reference the same URL.
What are hreflang tags?: Hreflang tags tell search engines which language/region version of a page to serve to users in different locations. For example, a site with English and French versions uses hreflang to ensure French-speaking users see the French version in search results.
What does the robots meta tag do?: The <meta name="robots"> tag controls whether search engines index the page and follow its links. Common values include 'index, follow' (default), 'noindex' (don't add to search index), 'nofollow' (don't follow links), and combinations thereof.
Can I check a URL directly?: Yes, if the target site allows cross-origin requests (CORS-permissive). Many sites restrict this for security reasons. If the URL fetch fails, you can view the page source manually (Ctrl+U in most browsers) and paste it into the HTML tab.
Does this tool support dynamic pages rendered with JavaScript?: No: this tool parses the raw HTML response, not the JavaScript-rendered DOM. For JS-rendered pages, you would need to copy the rendered source from browser DevTools (Elements panel → right-click → Inspect, then copy outer HTML).
Is this tool free?: Yes, completely free with no account required and no usage limits.

AlteredIdea vs alternatives

vs browser extensions: No install required, works on any device including mobile.

vs manual inspection: All tags surfaced and conflict-checked in seconds instead of searching through source code.

vs paid SEO tools: Completely free, no account, no subscription.

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