What Is a Canonical Tag and How to Check Yours in 30 Seconds

A canonical tag is a line of HTML that tells search engines which URL is the master version of a page. Without one, Google can treat your http and https versions, or your www and non-www versions, as duplicate pages and split your ranking power between them.

When you need a canonical tag

Every indexable page needs a self-referencing canonical tag pointing to its own URL. You also need cross-domain canonicals when the same content exists on two domains. Most canonical problems come from site templates that omit the tag entirely, which is why 41% of the pages we audited failed this check (see the full data).

How to check yours in 30 seconds

Open the page, view source, search for "rel=canonical". If nothing appears, your page has no canonical and risks duplicate indexing. Or run the free On-Page SEO Checker, which fetches your live HTML and reports the canonical status alongside 14 other ranking factors.

The three canonical mistakes that hurt rankings

• Missing tag entirely. Google guesses, and guesses badly on parameter URLs.
• Canonical pointing to a redirected URL. Pick one final address and stick to it.
• Canonicalizing every page to the homepage. This tells Google your whole site is one page.

Bottom line

Canonical tags are a five-minute fix with permanent upside. Check yours before anything else on this list, and use the internal linking checker to make sure Google can actually reach your canonical pages. For the full checklist, read the 15 on-page factors that actually matter.

Frequently Asked Questions