All About Canonical Tags

When search engines crawl many URLs for duplicate content, it causes a number of SEO problems. Having pages of identical or very similar content on your website may cause a search engine to devalue your website when determining rankings. Using canonical tags will help you control these duplicate content issues and take full advantage of SEO practices.

A canonical tag is a special tag inserted into the header of an HTML that lets search engine “bots” know the page contains original content, and is not just a duplicate of another page. Major search engines have supported the use of canonical tags for years, however, despite the benefits it offers to site operators and users (e.g., SEO rankings), many site operators have yet to implement it. This reluctance is most likely attributed to a lack of knowledge regarding the tag and its purpose.

Why Do Canonical Tags Matter?

You might be thinking that canonicalization isn’t really something to cause major concern. The problem is that search engines operate on the assumption that every unique URL is a separate page. Many sites automatically add tags, allow multiple paths to the same content, and add URL parameters for searches; so, you may have several of duplicate URLs on your site and not even realize it. There are also some times where your homepage may be the preferred URL, but try to avoid this if possible. If all your canonical pages point to your homepage, none of your webpages will be crawled and indexed by search engines.

Here are a few examples of how multiple URLs on a site may be seen as duplicate content:

·         Multiple URLs or Category Views: If you have an ecommerce website that offered multiple ways to view products based on categories (i.e., men’s shirts, women’s shirts, kid’s shirts), and these offer the same results through filter options, duplicate content- at least in the eyes of web crawlers– is created.

·         Cases: Users and browsers treat upper and lower case the same and have become largely interchangeable. However, the same is not always true for search engines, so if a website mixes up case in filenames, duplicate content- at least in the eyes of web crawlers– is created.

·         Mobile URL: Typically, if there is a separate mobile template website that is on a sub-domain or sub-directory, duplicate content- at least in the eyes of web crawlers– is created.

·         Country URL: When using multiple country-specific URLs, the content largely remains the same, it is just in a different language, therefore, duplicate content- at least in the eyes of web crawlers– is created.

·         Tags in Blogs: If multiple blogs on your site are labeled with the same tags, they will show up in all of the same tag categories, creating duplicate content- at least in the eyes of web crawlers– is created.

A canonical tag is used in all these instances to tell search engines which is the original content, and which URL should be crawled, indexed, and returned on search engine result pages (SERPs).

How to Correctly Use the Canonical Tag

First, decide which URL is preferred, and then add the following mark up to the <head> section of the preferred URL:

<link rel=”canonical” href=”” />

Luckily, most CMS have this built in, or have plugins available to automate most of the process. If you are not using a CMS, search engines use the following to help manage the process:[1]

·         Selective use of 301 redirects. Once a 301 is in place, a user won’t land on the duplicate URL and will be redirected to the canonical version.

·         Use Google Webmaster Tools to identify how to handle precise URL parameters.

·         Add HTTP headers using PHP and/or .htaccess (inserting the header () function in front of any HTML) to tag on a HTTP header rel=”canonical” link to the actual header.

Common Mistakes in Applying Canonical Tags

Each page must only have one canonical link specified in the <head>. If your canonical link appears anywhere but the <head> section (such as in the body), it is simply ignored by search engines. The canonical link should appear as early as possible to avoid this issue. Other places to avoid adding multiple canonical links are:[2]

·         Using Canonical Links on Paginated Results: When splitting content over multiple pages, use rel=prev and rel=next tags instead of rel=canonical to ensure that each page is indexed by search engines. Alternatively, if you consolidate the content onto a single “View All” page, you just can place one rel=canonical on that page instead of three or four across multiple.

·         Using Canonical Links in Featured Articles: If your website includes a regularly updated “featured article”, avoid using the rel=canonical tag on this page; otherwise, this page may be ignored and not appear in search results.

·         Using Canonical Links Instead of 301 Redirects: Although a canonical link appears very similar to a 301 redirect (they both tell search engines to treat multiple URLs as a single page), they are different in terms of metrics. A 301 redirects all traffic to a specific URL and a canonical tag gives credit to the original page.[3]

Canonical Tag Best Practices

So, what pages should have canonical tags? The answer: as many as appropriate. Visits from inbound links (i.e., social media, internal site search, or referral links) may generate a unique URL that could negatively affect your site’s SEO rankings.[4] Additionally, it’s okay if a canonical tag points to the current URL; many CMS allow multiple URL paths to access the same content.

Avoid Mixed Signals

Do not canonicalize page 1 –> page 2 and then page 2 –> page 1 or 301 redirect page 2 -–> page 1.[5] Send clear signals or you force search engines to avoid a canonical tag or misinterpret it. It’s also generally a good idea to avoid chain canonical tags (1–>2, 2–>3, 3–>4), this is considered bad practice.

Be Cautious When Canonicalizing Near Duplicates

When you think of canonicalization, you probably think of exact duplicates, but be wary when using a tag on near-duplicates—if the pages are too different, SEOs may ignore the tag.[6] Most of the time, the content isn’t actually copied, but multiple URLs redirecting to the same content. True duplication is the process of content appearing on multiple unique URLs.


While the odds of being punished for housing duplicate content is unlikely, search engines indexing all of your duplicate content affects the relevancy of their results as well as your page rankings, site traffic, and revenue. If you haven’t introduced canonical tags to your site yet, first look to see if you have duplicate content (or multiple URLs pointing to the same content), before applying the tags. If you already have canonical tags, reexamine the implementation to ensure it was all done correctly, and no pages are hiding from SEO indexing.

If you aren’t sure if issues with canonical tagging are affecting your website’s SEO, Divergent Web Solutions can perform a full SEO Audit to identify any issues that affect how your site is crawled and indexed. Once the issues are identified, you can start fixing them. Contact us today!


Divergent Web Solutions creates high-quality websites and is a full service web-presence firm, which supports small businesses, by creating space and focusing on their design, marketing, social, and/or development platforms where they do not have to pay the price of hiring a custom developer. Contact us for a free consultation, and we’ll develop a customized quote tailored just for your unique needs and budget at

[1] Information taken from “A Beginners Introduction To The Canonical Tag,” Unamo 2014, URL:

[2] Information taken from “A Beginners Introduction To The Canonical Tag,” Unamo 2014, URL:

[3] Information taken from “A Beginners Introduction To The Canonical Tag,” Unamo 2014, URL:

[4] Information taken from “What Is a Canonical Tag and How Can It Help Your SEO?,” Lieberman Technologies 2014, URL:

[5] Information taken from “Canonicalization,” Moz 2017, URL:

[6] Information taken from “Canonicalization,” Moz 2017, URL:

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