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Canonical Tag Checker

Check any URL for canonical tag issues that cause duplicate content problems and dilute your page's search ranking signals.

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Common canonical scenarios.

When to canonicalize, what the tag should look like, and what happens if you get it wrong.

Standard page

Self-reference its own URL. Risk if wrong: URL parameter variants eat your ranking

Paginated list (page 2, 3, …)

Each page self-references. Risk if wrong: Pagination collapses, deep pages disappear

Product color variants

Variants canonical to the main product. Risk if wrong: Variants compete, none ranks

Printer-friendly page

Canonical to the regular page. Risk if wrong: Google indexes the print version

Syndicated article

Canonical to the original on your site. Risk if wrong: Republished copy ranks, yours doesn't

HTTPS migration

All canonicals use https://. Risk if wrong: Google indexes the http:// version

Tracking params (UTM, etc)

Canonical to the clean URL. Risk if wrong: Every campaign creates a duplicate

What is a canonical tag?

A canonical tag is a <link rel="canonical" href="..."> element in the <head> of a page (or equivalently, an HTTP Link header) that tells search engines which URL is the authoritative version of a piece of content. When the same or near-identical content lives at multiple URLs - product variants, UTM-tagged campaigns, paginated series, print views, mobile subdomains - the canonical tag consolidates all the ranking signals onto a single URL.

This checker fetches any public URL, extracts every canonical signal (HTML tag, HTTP Link header, and robots directives), and flags the issues Google is most likely to treat as self-canonical violations: missing tags, multiple conflicting tags, relative URLs, cross-domain mismatches, and the dreaded noindex + canonical combination that causes Google to drop both signals.

Always self-reference by default

Every indexable page should have a self-referencing canonical. It's the cheapest protection against URL-parameter duplication you didn't anticipate.

Use absolute URLs

Canonical hrefs should always start with https://. Relative URLs sometimes resolve in unexpected ways on pages served under different base paths.

One canonical per page

Multiple canonicals pointing to different URLs cause Google to ignore all of them. If your CMS and SEO plugin both inject a canonical, disable one.

Never combine noindex + canonical

If a page is noindex, drop the canonical. Google may use the noindex to de-index the canonical target too. Pick one directive.

Frequently asked questions.

What is a canonical tag?

A canonical tag is a <link rel="canonical" href="..."> element in the <head> of an HTML page that tells search engines which URL is the master version of that content. When identical or near-identical content exists at multiple URLs (product variants, tracking parameters, print versions, paginated series, etc), the canonical tag tells Google to consolidate ranking signals into a single URL.

Why does my canonical tag matter for SEO?

Without canonicals, duplicate or near-duplicate URLs compete against each other. Each version gets partial credit, none ranks as strongly as a unified version would, and Google may pick a random URL as the canonical - sometimes the wrong one. A correct canonical consolidates link equity, prevents index bloat, and ensures the URL you want to rank is the one Google indexes.

What is a self-referencing canonical?

A self-referencing canonical is a canonical tag that points to the URL of the page it's on. For example, https://example.com/about having <link rel="canonical" href="https://example.com/about">. Self-referencing canonicals are considered best practice even on pages without duplicates, because they protect against URL-parameter-based duplication (UTM tags, session IDs, etc) that you may not have anticipated.

Can a canonical tag hurt my SEO?

Yes, if set up incorrectly. The classic mistakes are: pointing every page to the homepage (which hides all your content from Google), using relative URLs that resolve to the wrong target, or pointing to a noindex URL. Another common issue is canonicalizing product variants to a page that returns 404. Always verify canonicals after major CMS changes or platform migrations.

Does Google always respect the canonical I set?

No. Google treats canonical tags as a strong hint, not a directive. If your canonical contradicts other signals - internal links, sitemap entries, redirect chains, or content similarity - Google may choose a different URL as the canonical. Search Console's 'Indexing > Pages' report tells you when Google picks a different canonical than the one you specified.

Can I canonicalize to a different domain?

Yes, cross-domain canonicals are valid and work well for syndicated content. If you republish an article on Medium or a partner blog and include a canonical pointing to the original URL on your site, Google will consolidate ranking signals to the original. This is the preferred way to syndicate content without creating duplicate content penalties.

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