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How-to 12 min read

How to use rel="canonical" tag for SEO

How to use rel="canonical" tag for SEO
How to use rel="canonical" tag for SEO

Stacy Mine
Editor at Serpstat
Duplicate content has a detrimental impact on your website's ranking on Google. It's just common sense. No wonder fixing duplication issues is one of the most important aspects of site optimization.

Webmasters often use a 301 redirect as a method of solving this problem, however, it's not always an option. That's where the canonical tag comes into play. It indicates the main page among its copies within a website, which gives the search engine a powerful signal to set its priorities straight.

Not using this simple way of fixing the (inevitable) issue of duplicate content on your website, and therefore, boosting your SEO efficiency, would almost be a crime.

So let's get straight to the point and answer all the most common questions.

What is a canonical tag?

The rel canonical tag (rel="canonical") is a piece of HTML code that specifies the most important version out of the bunch for pages with identical, nearly the same, or very similar content. To put it another way, if you have duplicate content on multiple URLs, you choose one "canonical" version and point the search engines at it, while the rest gets marked as "additional".

What are canonical pages?

If the website includes pages with duplicate content, only one of them will be shown on SERP. If you don't specify it yourself, it will be randomly selected by the robot. The term "canonical" refers to this specific type of page, the one that ends up appearing in search results.

By using the link rel="canonical" attribute, you're giving an instruction to search engine robots, which of the duplicate pages is preferred, and supposed to be canonical, rather than allowing them to pick it randomly.

How does rel="canonical" work?

The canonical tag is a signal for search engines to start considering the page's priority. It can be placed on any HTML-page between the <head> and </head> tags.

When there are identical or extremely similar pieces of content under different URLs on your website, using the canonical tag will mark the master page, which will be the one shown to search engines, and to users on SERP.

All the other pages search robots will consider additional, and if you use the canonical tag properly, all their characteristics are going to be directed to the canonical page, e.g. links, visitors' behavior.
SEO Rel Canonical scheme for Google

Canonical tags vs 301 redirects

What is definitely going to complement your SEO strategy? The answer is simple: you should always redirect when it's needed. However, in some cases it isn't always the best and easiest way to go, for the following reasons:

  • its time-consuming realization process;
  • some pages are regularly used by visitors
In this case, you should certainly set a canonical URL if you don't want to get in trouble with the search robots.

Advantages of the rel="canonical" for SEO

Search engine robots have a very negative attitude to the content they deem duplicate. They refuse to index identical text, whether it comes from different websites, or from pages within the same domain. Solving this issue is an essential aspect of an effective internal site optimization.

Making the content noticeable for users leads to an increase in visits and positively influences the site's conversion. A canonical URL can also refer to another domain if the content on these pages is the same.
Rel canonical structure chart

How exactly do you set up rel="canonical"?

Canonical URLs can be specified by using different methods. We want to introduce the best ways for canonicalization, keeping things simple and organized:

#1 On the page: HTML tag (rel=canonical)

The easiest and most obvious way to specify canonical pages is pasting the rel="canonical" attribute into the code of the page. Just insert the piece of code into any duplicate page's <head> section.
<link rel="canonical" href="http://your-website.com/canonical-page.html"/>
Keep in mind: The tag must be placed in <head> </head> section. If you accidentally set the tag someplace else, it will simply be ignored by the search engines

#2 HTTP header

There is no <head> section in some documents, so it's impossible to place canonical tags in the page header. To set canonicals in such instances, you'll need to use HTTP headers. On ordinary webpages, you may also implement a canonical in HTTP headers.

#3 XML-sitemap

Sitemap is also a great way to point search robots at the pages on your website that are the most essential. Sitemap URLs are a simple approach to define canonicals for a large website.
However, there is a slight chance that search engines could ignore the tag.

#4 Server's response

This option is suitable for non-HTML formats. For instance, if you need to index a PDF-document, you can add the rel="canonical" attribute to the http. In this case, the server will show the following thing:
Link: <http://your-website.com/main-file.pdf>; rel="canonical"
The only issue is that Google currently supports <link> element for web search only.

The main mistakes of using rel="canonical"

1
rel="canonical" is used for the first page of a pagination series

A website's article can consist of many pages. Since the second, third, and all subsequent pages of the article are not duplicates, using the rel=canonical attribute to designate the first page as canonical would be erroneous. In this situation, a search engine error will prevent pages 2 and 3 from being indexed altogether.
2
Absolute URLs are mistakenly taken for relative

Absolute URLs require the full address, including http://.
If a webmaster mistakenly puts example.com/shoes.html instead of http://example.com/example.com/shoes.html, search engines may ignore the rel=canonical tag.
3
Unintentional use of rel="canonical", attribute use on multiple pages

When webmasters replicate the page template, they often forget to modify the attribute. These errors are accidental, but they may lead to severe negative repercussions.
4
A page section links to a specific article

If you have numerous areas on your website where you publish several articles daily, the content of the section page is identical to that of the article page. To eliminate duplicates, use rel="canonical" to make the article page the canonical version. In this case, it is advisable not to set attributes at all, since the search engine will not display a page with a section in the results.
5
rel="canonical" is used in body

The rel="canonical" attribute should only be included in a head section of an HTML document. If it falls into the body section, search engines tend to ignore it.

Rules for specifying canonical links

As you can see, when using canonical links, webmasters can make plenty of mistakes, which could cause serious problems and traffic loss. To avoid them, you have to follow these rules:
1
One page — one rel="canonical" tag in <head> section.
2
Make sure that the tagged page has been indexed.
3
Don't complicate the link structure by building chains of canonical URLs.
4
If you tag a page using several methods, be sure that all the links refer to the same page.
5
Choose absolute links instead of relative ones. It will minimize errors and prevent search engines from ignoring the pages:

Wrong: <link rel="canonical" href="shop.com/tables.html" />
Correct: <link rel="canonical" href="http://shop.com/tables.html" />

Correct examples of using rel="canonical"

Despite it being a quite useful tag, using isn't always reasonable. There are several particular cases when the canonical pages are definitely needed:
1
Search in online-shops

Canonical is a must when it comes to the search catalog in an online store.

Let's illustrate it with an example: different people find the same goods by using various search methods. Person 1 is looking for a pair of shoes by choosing the brand or model. At the same time, Person 2 finds the same list of shoes via setting a particular price range or rating. Both of them land on pages with the same content, but the page URLs are actually different.

To solve it, just pick one main page, and refer all the other ones to it, simply by tagging them with the canonical attribute.
<link rel="canonical" href="http://online-shop.com/tables.html"/>
2
Several goods of the one type

This situation is also related to online stores.
For instance, you might have a list of practically same goods, only differing by color. It is better to choose one of them as canonical and bind other ones to it, otherwise the bots will consider such pages to be duplicate content.
3
Loyalty program for clients

If there is a loyalty system on your site which includes bonuses, discounts, and special offers for frequent customers, create links with rel="canonical" on pages for special clients and direct them to the standard ones.
4
Pages of pagination

Pagination creates duplicate content. If there is a «View all» page on your site, refer all the connected URLs to it.
5
Work with the UTM

If you use the UTM to monitor the efficiency of your advertisement campaign, you need to remove doubles. Place the canonical link from the page with the UTM to to the basic page.
Sometimes it's pretty hard to understand what page should be considered the main one. The page has to be the most suitable for indexation. In order to make the right choice, it is better to look at these two aspects:

  • page traffic;
  • the number of the internal/external links.

Conclusion

With help of the rel="canonical" tag, you can manage content duplication on your website and show search engines what pages are should be indexed. The reasonable use of this instrument positively influences the site's indexing, ranking, traffic and conversion as a result.

As we've discussed, there are several methods of adjusting the canonicalization. Choose the most suitable one for you, and pay attention to details in order to use the tag properly and avoid the most common mistakes.

FAQ:

How do you check rel="canonical"?

You can check if the canonical pages are set up correctly by conducting a detailed SEO analysis. The results will reflect the pages without the rel="canonical" attribute, to which it should be added, and their corresponding canonical versions.

Should every page have a canonical tag?

To avoid any possible duplication, all pages (including the canonical page) should have a canonical tag. Even if a page has no other versions, it should have a canonical tag that links to it.


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