Let me introduce SEOs to a fabulous tool in the arsenal: the Canonical Tag. The rel=canonical tag was implemented in 2009 by Google to solve duplicate content issues. Canonicals have been around for a long time, but there is still a lot of confusion in the SEO community on how to use them. More importantly, there are some very cool things that SEOs can do with canonicals to gain a ranking advantage.

What is Rel=Canonical?


Canonical: accepted as being accurate and authoritative.

The intent of the tag is to tell Google that “this page is duplicate content. The original content is at this other URL. Please rank that page and ignore this page.” The canonical tag looks like this:

<link rel=”canonical” href=”https://www.yourdomain.com/page-name” />

and he canonical link element can be either used in the HTML <head>, or sent with the HTTP header of a document.

The URL in quotes is the target, and will be viewed by Google as the original URL and “canon”.  These Matt Cutts Video are old, but they are still valid.

Here are the pertinent facts about rel=canonical:

  • Google views the tag as “a strong suggestion”. Google doesn’t guarantee that they will honor the tag, but I’ve never seen an instance when Google hasn’t.
  • Bing doesn’t give a straight answer on whether they honor canonical tags, and instead recommends “URL Normalization” through Bing Webmaster Tools.. I can tell you from experience that Bing doesn’t do a good job recognizing cross domain canonicals.
  • It’s OK to have a page canonical to itself. Many eCommerce sites do this so that when a page with a parameter is created, the canonical tag is automatically on the page.
  • The content on the page needs to be very close to the the target URL. I’d recommend better than 90% duplicate to be safe.
  • If Google honors the rel=canonical tag, it functions almost exactly like a 301 Redirect in terms of ranking power. About 95% of the “Link Juice” is transferred to the target page even though the original page still exists.
  • The canonical tag transfers link juice within a domain, but it also transfers ranking authority across domains. If you choose to canonical across domains, be aware that you will be transferring +/-95% of the page’s link juice to another domain.
  • Google doesn’t have a penalty, per se for duplicate content. Duplicate content confuses Google’s algorithm, and as a result of Googlebot not knowing which page to rank, will not rank any of the pages strongly.

That information has been known for a while, but how can SEOs use canonicals to improve rankings?

  • (On-Site) eCommerce Products Appearing in 2 Categories: Many eCommerce platforms are duplicate content machines. For example, if a product resides in 2 categories, the CMS could create 2 URLs for the same product. Example: www.domain.com/category-1/widgets/, and www.domain.com/category-2/widgets/. This is duplicate content, even though it’s the same product. By placing the rel=canonical tag on one of those pages, Google will consolidate the ranking authority.
  • (On-Site) eCommerce Parameters: Other content management systems use tracking parameters. Ex: www.domain.com/product-name.html?clicksource=homepage. This is a distinct URL from the root URL (www.domain.com/product-name.html) and is also duplicate content. By placing the canonical tag on the parameterized version of the page, once again, Google will consolidate the ranking power of the pages.
  • (Off-Site) eCommerce Duplicate Content: I ran into this one first hand. We had a large ECommerce company that had multiple brands selling the same products. I couldn’t get either site to rank for anything, and keyword rankings would flip flop daily between the sites. Since both sites are significant brands, we couldn’t consolidate the sites under 1 domain. We canonicaled the sites together, and within a week, we started popping hundreds of keywords onto page 1.
  • Canonical Link Building: Instead of asking a webmaster to publish your content with a link, have them publish the content with a canonical tag to the exact same content on your website. A link will only pass some of the page’s link juice. A canonical tag will pass 95% of the page’s juice!!!
  • Canonical PBNs: This one is purely black hat, but if you have a PBN (Private Blog Network), you can use canonicals instead of links to rank your pages. Since the canonical tag passes 95% of the link juice, it’s far more effective than using your PBN for links. I wouldn’t go crazy with this one.
  • Ranking ECommerce Category Pages: This one’s a little on the grey side. Getting links to your ECommerce category pages is damn near impossible. So you created a dynamite blog post that generated a ton of links, just like you are supposed to. You put contextual links from your blog post to your category page to help it rank. How about duplicating the content of your blog post at the bottom of your category page, and using a canonical tag in your blog post to transfer all of the link juice to the category page? It’s better than using a 301 since you can leave the blog post in place for a better UX.

There are a number of WordPress plugins including Yoast SEO that make implementation a snap.