Canonical Tags

Canonical tags, also referred to as a “rel canonical” tag, is an HTML element that helps webmasters indicate to search engines which URL represents the “master” version of a web page.

In other words, the canonical tag tells Google or Bing: “Hey search engine, ignore the other duplicate versions of this content and focus on this main URL.”

Here is what the actual HTML canonical tag code looks like:

Why Canonicalization Matters

Many websites end up with duplicate content issues, even if they don’t realize it. For example, your homepage could be accessible through:

  • http://www.example.com
  • http://example.com
  • https://www.example.com

And that’s just a few common examples. Dynamic URLs, multiple paths to the same content, pagination, URLs with different parameters, and more can create duplicate content at scale.

From a human perspective, we know all those homepage URLs are pointing to the same destination. But search engines see each unique URL as a separate page to crawl, index, and try to rank.

This duplication causes three core problems:

  1. Crawlers waste time crawling duplicate versions of pages, rather than unique content.
  2. Ranking signals get diluted across too many duplicate URLs.
  3. Search engines may index and rank the wrong version of a duplicated page.

By implementing canonical tags, you tell Google which URL is the definitive version to show in search results. This prevents duplicate content issues.

Best Practices for Canonical Tags

Here are six key canonical tag tips:

  1. Self-referential canonicals are fine. It’s okay for a page’s canonical tag to point right back to itself.
  2. Spot-check dynamic canonical tags. Bad code can incorrectly generate different canonicals.
  3. Don’t send mixed signals. If Page A canonicalizes to Page B, don’t also redirect or canonicalize Page B back to A.
  4. Use caution when canonicalizing near-duplicates like product pages. The pages should be very similar.
  5. Canonical tags can be used cross-domain if you own all sites. This focuses on ranking ability.
  6. Canonical tags pass equity, unlike 301s. But remember: canonicals allow visiting both URLs, unlike redirects.

In some cases, using 301 redirects instead of canonical tags makes more sense. With 301s, visitors only see one version of the content.

How to Audit Canonical Tags

When auditing canonicalization, check that:

  • The page has a canonical tag
  • The canonical URL points to the correct destination
  • The canonical page is indexable (not blocked by robots.txt or noindex)

Use the MozBar browser extension to easily check pages for proper canonical tag implementation. For bulk audits, tools like Moz Pro crawl your pages at scale to surface missing canonical tags.

By properly canonicalizing your website to consolidate signals on the right URLs, you can solve duplicate content issues and strengthen your overall SEO strategy.

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