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What is a Canonical Tag and What Uses?

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Preface What is a Canonical Tag or Canonical Link?

The Canonical tag is a way of announcing to search engines that a URL is a copy of another homepage. Canonical tags can avoid problems such as duplicate contents that occur with some URLs. More practically, a Canonical tag specifies the version of the URI we want to display in search engines.

canonical tag

Why is it important to use the Canonical tag?

As we mentioned in the duplicate contents article, when the search engines see lots of URLs with the same content, we won’t get good results on the site’s SEO. First of all, when search robots keep track of duplicate contents, they will probably lose some of your proprietary content. Secondly, a large amount of duplicate content reduces site rank. Finally, if the search engines want to show URI among the duplicate pages in the search results, they will probably choose the wrong version. In general, canonicalization, or the use of the Canonical tag, ensures that the duplicate contents are properly managed.

URL Problems

You might be wondering why anyone would want to create a duplicate page and don’t skimp on using the Canonical tag by sketching this assumption. The problem is that we humans keep the pages as a concept in our minds, but the search engines consider every URL to be a new page.

For example, search robots will probably access your site through the following sample URLs:


From the human point of view, all of these addresses are the same page, but for search engines, each of these addresses is a separate page. Only in this example and for the first page of a site can five different addresses be mentioned. In the real world, this is just a small example of these changes in URLs.

Modern content management systems and many dynamic code-based websites exacerbate this problem. Many sites automatically add many tags to the URLs, resulting in many URLs for the same content. Search parameters, categories, and monetary units are also other factors for changing URLs. With this description, you realize how serious the problems of duplicate contents are on websites.

Solutions for using the Canonical tag

The duplicate contents problem can be very tricky, but there are some important things to consider when using the Canonical tag:

1. Canonical tags can be referenced on their own

There is no problem using the Canonical tag about the current address. In other words, if you have a home page and two duplicate pages, in addition to referring to the Canonical tag in two duplicate pages, you can also refer to the home page itself.

canonical tag

2. Be sure to place the Canonical tag on the home screen

Since the problem of duplicate pages is very common for the homepage of the site and users are linking to your homepage in various forms, it is recommended that you place the Canonical tag on the homepage to avoid unexpected problems.

3. Check Canonical tags manually

Occasionally it is found that incorrect codes and problematic modules, especially in content management system storefronts, provide different reference URLs for each of the duplicate pages, which contradicts the principle of working with this tag. Is. Take a look at page codes every other day to make sure this is not the case.

4. Avoid nested signals

Search engines do not consider Canonical tags that have been used inappropriately. In other words, avoid referencing page A to page B and then referencing page B to page A using the Canonical tag. And things, like referring page A to B and then redirecting page 301 to page B to A, are also not correct. It is also incorrect to use the Canonical tag in long chains (A- -> B, B -> C, C -> D). Give the right signal to search engines, otherwise search engines make unpleasant decisions for your website.

5. Be careful about using the Canonical tag on roughly similar pages

When it comes to canonicalization, most people think of identical pages. Canonical tags are used on roughly similar pages, but they should be used with caution. There are a lot of comments on this in general, but use on very similar pages is no problem. For example, on pages related to a product that has URLs that are different solely because of parameters such as user location or product color, using the Canonical tag is not the case. This tag may be ignored by search engines if there is a large difference in the content of the two pages.

6. Master the Canonical tag across multiple domains

If you own several websites, you can use the Canonical tag between domains. Suppose you publish content for one site and post it to other websites with the Canonical tag. Using the Canonical tag on other websites will transfer the credentials to the same page. Please note that this type of Canonical tag prevents search engines from ranking for this page. So if this is okay with your business rules, use it.

Compare Canonical and Redirect 301 tags

One of the common questions in using Canonical Unique is whether this tag, like Redirect 301, fully validates the page. In many cases it may seem like the page’s credentials are being transferred to the Canonical tag, but the answer to that question is always a bit skeptical. Keep in mind that these two techniques have two different outcomes for users and search engines.

If you redirect to page A to page B 301, users will automatically be redirected to page B and will not see page A. If you refer to page B using page Canonical, search engines know that page B is the homepage, but users can still view page A and B. Consider the working conditions and limitations to decide on one of these two solutions.

canonical tags

Canonical tags are not that complicated. They are just hard to understand at first.

Remember that canonical tags are not a directive but rather a signal for the search engines. In other words, they can choose a different canonical from the one you declare.

You can use the URL Inspection tool in Google Search Console to see both the user-declared and Google-selected canonical.

duplicate content


Here are the classifications used by Google in the Google Cover Console index coverage status report for canonical URLs:

  • Alternative page with the appropriate canonical tag. This shows the pages where you specified another page with a canonical tag and it was respected. It works as expected to consolidate the page you have chosen.
  • Duplicate without canonicality selected by the user. There are duplicate pages and none have a canonical chosen. In this case, Google has chosen one for you. If it is not the one you prefer, you must add a rel = canonical tag.
  • Duplicated, Google chose a canonical different from that of the user. This shows cases where Google chose to ignore your canonical proposition but still chose a different version to display in the index.
  • Duplicate URL not selected as canonical. This is also the case for a canonization signal (submitted in a site map) ignored. There is no canonical URL explicitly marked in this set of duplicate pages and in this case Google believes that another URL next to the one you submitted should be displayed in the index.


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March 23, 2020
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