Canonical Tag Checker

A canonical tag is a small line of HTML in the head section that tells search engines which URL is the master version of a page when duplicates exist. The format is <link rel='canonical' href='https://example.com/page'>. It's how you tell Google 'consolidate ranking signals to this URL, ignore the others'. Common uses: parameter URLs, tracking variants, mobile/desktop pairs, paginated content. Wrong canonical setups cause more silent SEO bugs than almost any other on-page issue, so always verify after any URL change.

They consolidate duplicate content signals into one URL so your authority doesn't get split. Without canonicals, two URLs (with and without the ?utm parameter, for example) compete with each other in search and dilute backlinks. A working canonical funnels everything to the master version. Real example: an e-commerce site with parameter URLs was splitting links across 12 versions of the same product page. After canonical fixes, that page jumped from position 14 to position 5 in eight weeks.

A self-referencing canonical is a canonical tag that points to the URL of the page itself. So example.com/blog/post has <link rel='canonical' href='https://example.com/blog/post'>. It's a defensive practice — it tells Google 'this is the master version' even when no obvious duplicate exists. Useful because parameter URLs and session IDs can show up unexpectedly. Most SEO plugins set this by default. Verify with the Canonical Tag Checker after every theme change or migration.

Three options. View page source and search for 'canonical' — the link tag will be in the head. Use a browser extension like SEO Pro Extension. Or paste the URL into our Canonical Tag Checker for a clean readout including the canonical URL, status, and any conflicts (like a canonical pointing to a noindex page or a 404). Use the third option when auditing across many URLs — it's faster than View Source and shows issues you'd miss by eye.

Yes, this is called a cross-domain canonical and it's perfectly valid when the same content appears on multiple domains. Example: if you syndicate an article from blog.brand.com to medium.com, the Medium version should canonical to the original on blog.brand.com. The HTML looks like <link rel='canonical' href='https://blog.brand.com/article-slug'>. Use it carefully — don't canonical your site's pages to a competitor's site or you'll lose all the ranking value. Always verify the destination URL is live and indexed.

Google has to guess which version of a duplicate set is the canonical. Sometimes it picks correctly; sometimes it picks a parameter URL, the http version, or the wrong subfolder. Symptoms: rankings split between similar URLs, the wrong URL showing in the SERP, or sudden drops after a CMS update. The safer practice is to always have a canonical — even a self-referencing one — on every indexable page. It removes ambiguity and prevents a whole category of avoidable SEO bugs.

It's a hint, not a directive. Google treats canonical tags as a strong signal but reserves the right to ignore them when the evidence points elsewhere — for example, if your canonical points to a 404, a noindex page, or a clearly less-authoritative URL. The common misconception is 'I set the canonical, the job is done'. Real example: a client set canonicals to the desktop version, but Google chose mobile because of mobile-first indexing. Always check Search Console's URL inspection to see Google's chosen canonical.