Using Rel=Canonical Tag For SEO-Friendly Cross-Domain Duplicate Content

Aaron Farr
By Aaron Farr

What Is a Canonical (Or Rel=Canonical) Tag? Why Is It Important?

A canonical tag (also known as a “rel=canonical” tag) is a tried-and-true method of letting online search engines know that a specific URL represents the “master copy” of a website page. Implementing the canonical tag can prevent problems that are typically caused when identical or “duplicate” content appears on multiple URLs. Essentially, the canonical tag notifies search engines which version of a URL you want to appear in its search results.

In addition to negatively impacting your SEO rankings, duplicate content can cause some other pretty serious SEO problems if not addressed swiftly, properly, and thoroughly. When a search engine “crawls” multiple URLs with identical (or nearly identical) content, several of these SEO problems can unfold.

First and foremost, if search engine crawlers have to dig through an excessive amount of duplicate content, they might miss a good portion of your original content. Secondly, large-scale duplication can really knock down and diminish your ranking abilities. Even if your content does rank, the search engines might mistakenly identify the incorrect URL as the “original” URL – especially if you have not used canonical tags to “educate” the engines and their crawlers. When confronted with duplicate content, the confused crawlers employed by the search engines simply don’t or won’t know which versions of the duplicate content to rank for query results – nor which versions to include and exclude from their indices.

Related: Technical SEO Checklist & Guide 

Content management systems (CMS) and dynamic, code-driven websites amplify the problem further. Many sites automatically add tags, enable multiple paths and URLs to the same content, and add URL parameters for sorts and searches. It’s possible that you currently have hundreds, or even thousands of duplicate URLs on your site – without ever realizing it. Well, you may not know it. But the search engines and their crawlers sure do.

Utilizing canonicalization and canonical tags helps you control your duplicate content – and empowers your site and content to perform better and more efficiently on the increasingly-crowded web. Think of smart rel=canonical usage as a win-win.

How Do Canonical Tags Differ From 301 (Permanent) Redirect?

In many cases, canonical tags pass link equity (PageRank, Authority, etc.) much like 301 (permanent) redirects. However, canonical tags and 301 redirects create two vastly different results for search crawlers and site visitors alike. For example, if you use 301 redirect to redirect one page to another, then human visitors will automatically be taken to the second page – without ever seeing the initial page. If you use canonical tags for the same page redirect, however, search engines will understand that the second page is canonical – but human visitors can visit both URLs, should they so choose.

How to Correctly Handle Duplicate Content With Canonical Tags

Like any tool involving any technology, there’s right and wrong – or smart and not-so-smart – ways to implement canonical tags in your ongoing efforts to handle duplicate content and its many unpleasant side effects.

First off, it’s important to decide which content or page you want to direct your viewers – and the search engines and their crawlers – toward. Remember that search engines, when faced with duplicate content, tend to “grab” one version – while filtering the others out. This also happens when and where multiple domain names are involved.

Once that primary decision has been made, you should decide whether it serves you, your business, and your site (and its content) best to use a canonical tag – or to opt with a 301 redirect instead. Remember, use of a canonical tag makes it possible for human visitors to visit both URLs, should they so choose, in the case of a page redirect. With 301 direct, the viewer is automatically taken to the secondary/redirected page.

Cross-Domain Usage of Rel=Canonical

What’s more, you can even use rel=canonical across different domains. In other words, you can have one “canonical URL” (or “preferred” version of a web page) replicated on more than one other domain – allowing you to, for example, distribute certain content across several sites.

Yes, multiple domains and pages can point to anyone “canonical URL” of yours.

Using the rel=canonical tag to tell the search engines that identical content exists on more than one domain not only can help you “cross-post” content across various domains that you own, but could benefit you when others republish your own unique content or rent or purchase content on other sites.

For some sites, businesses, and brands, there are strong, smart reasons to duplicate content across various site under their control. And Google fully supports cross-domain rel=canonical usage to help facilitate such efforts – via the rel=”canonical” link element established in 2009.

The rel=canonical element – often referred to as the “canonical link” – is a HTML element that helps webmasters prevent duplicate content issues. It does this work by specifying the “canonical URL,” and smart usage of the rel=canonical element also improves a site’s SEO performance and ranking.

The webmasters over at Google suggest you first choose your preferred domain, then place your focus on handling duplication (r.e. consolidate duplicate URLs) within your site before starting in on cross-site duplicate content efforts. Google then suggests you enable crawling and use 301 redirects where possible. According to Google, 301 redirects are “generally the preferred method, as it gives clear guidance to everyone who accesses the content.” The SEO experts at Yoast seem to agree here, advising that “if there are no technical reasons not to do a redirect, you should always do a redirect. If you cannot redirect because that would break the user experience or be otherwise problematic: set a canonical URL.

Finally, Google suggests that you now go ahead and use the rel=”canonical” link element, but be aware that there are situations where it’s not possible nor easy to set up redirects – such as an attempt to move your website from a server that doesn’t feature server-side redirects.

Cross-Domain Rel=Canonical Best Practices

If you’re going to use cross-domain rel=canonical, you do need to follow certain rules and “best practices” throughout the foundational process.

First and foremost, the page content needs to match – including not just text, but any images and embedded videos you may have on your “canonical URL.” The headline doesn’t have to match, but it helps if it does. The same goes for the links within the content. The title of any written piece of content, the navigation, and any site branding do not have to match to ensure cross-domain rel=canonical success.

Another step you should take here involves choosing which domain should get the SEO benefits and rankings when you decide to run duplicated content across multiple domains. Also, if a publication wants to re-post your content on their domain, you should ask for their re=canonical – instead of, or in addition to, a link back. In other words, you want it to come from their site to your site.

Examples of Smart Rel=Canonical Usage

Letting other sites post your content (and getting their re=canonical back in return) is just one of many examples of smart, efficient usage of rel=canonical in today’s online environment.

Posting the same blog post or other content pieces on an array of different sites and URLs, as we covered a good bit earlier, is another example. Another smart usage could involve using rel=canonical as a “compromise” for other, outside sites (i.e. sites not owned or controlled by you) that duplicate your content.

In summary, implementing the canonical tag can not only prevent the many problems caused by identical or “duplicate” content, but smart usage of rel=canonical can improve your site’s SEO performance and ranking. At the end of the day, who wouldn’t want to see those kinds of results?

Aaron Farr is a Sr. SEO Specialist at Power Digital with a passion for Technical SEO. He was born in Washington State and moved to San Diego to go to college for web design and video editing. Aaron has 6 years experience with Fortune 500 companies and loves the fast pace and ever changing environment that comes with it. He specializes in Schema Markup, Robots and XML Sitemaps. When not at work he loves playing video games, making candles, up-cycling beer bottles into glasses, and having fun with his two kids.