What Is Canonical Tag (+Its Benefits for SEO)?

What is a canonical tag?

A canonical tag (or rel = canonical) is a small piece of HTML code that helps search engines determine the “main” version of a page from the rest of the page that is the same or very similar.

In SEO, canonical tags are used to let Google know which version of a page you want to appear in search results, combining link equity from duplicate pages as well as improving your website’s crawling and indexing.

Here’s what a canonical tag might look like on a webpage:

<link rel="canonical" href="https://mangools.com/blog/robots-txt/" />

Why are canonical tags important in SEO?

The primary purpose of the canonical tag is to tell search engines which page is the original, the original version, and which duplicate look the same.

Generally speaking, websites usually have at least some pages that are considered duplicates – they display the same content but with different URLs.

In this case, Google will have to decide which page to choose for indexing and ranking – It will not use all pages as search results because they look the same or exactly the same ৷.

For example, product pages are usually not displayed by just 1 main URL. These may appear with different URL parameters that are frequently used (such as sort, currency, size, etc.):


In this example, the product page may appear in the main section – /clothes/, But will be filtered and displayed with size and color parameters. So it may appear as a search result under 3 different URLs.

This is where canonical tags become important – they will indicate to Google that you want to index the original URL section. /clothes/Use this as a search result and ignore the rest of the URLs

Note: Note that Google treats canonical tags as a signal – not as an instruction.

If there is a valid reason for choosing a page other than Canonical for indexing and ranking, search engines may completely ignore the Canonical tag:

Or as Martin Split puts it:

“Okay, let’s start with the idea that this is a guideline because it’s not.”

In addition to the basic purpose of the canonical tag, there are some important SEO benefits that come with it.

1. They combine PageRank

Canonical tags help combine link equity (PageRank) from all duplicate pages into one main, canonical page.

Duplicate pages can often get backlinks from various external sources – whether they are backlinks from random websites, social media users, etc.

These pages therefore partially occupy the link equity from the original version of the page – One that you actually want to rank as a search result.

By applying canonical tags to duplicate pages, PageRank can be moved to a single URL and thus improve its overall ranking in Google search.

2. They help manage syndicated content

Canonical tags tell search engines which websites contain the original version of the content And which websites only republish it (or syndicate).

Many website owners use other websites to publish their content (either for promotional or other purposes).

In this case, Google will have to decide which website should be the main source of this content and search results, and which websites only promote it.

Setting up canonical tags on these external websites helps to solve this problem and Promote the original, main version of the page in Google search.

Or as Danny Sullivan puts it:

3. They improve crawling

Canonical tags help search engines like Google to efficiently crawl the pages you actually want to crawl and index. – Unlike duplicates which should not be crawled at all.

Duplicate pages waste Google resources and time because they are not important for crawling or indexing purposes.

By employing canonical pages, Google will focus more on the most important pages and therefore save a “crawl budget”.

Or Google has officially said:

“The authentic page will be crawled regularly; Duplicates are crawled less frequently to reduce the Google crawling load on your site. “

How to add a canonical tag?

It’s easy to add canonical tags to your pages – Go to any duplicate webpage and page Add the rel = ”canonical” tag to the section.

The link to the canonical tag should point to the original version.

Canonical tags are best applied page by page. However, this can cost a lot of time and resources or be impossible even on large websites.

Fortunately, canonical tags can be applied automatically using various plugins such as Yoast SEO (for WordPress).

Implementing canonical tags with this plugin is quite simple:

  1. Select the page for canonicalization
  2. Go to the “Advanced” section of the page
  3. Add the canonical URL you want to specify
Yoast SEO example canonical tags

There are also several ways you can direct your canonical pages to Google

Use HTTP headers

Canonical tags can also be added to the HTTP header of a webpage.

This is especially useful for non-HTML documents such as PDFs – Since they do not contain any <head> Category where you can add a standard canonical tag.

To apply the canonical tag to the HTTP header, you need access .htaccess Attach your site’s file and canonical tag to a form that might look like this:

Link: <https://www.yoursite.com/random-document.pdf>; rel="canonical"

If you want to know more about adding canonical tags via HTTP headers, check out this article about canonical implementation.

Tip: There are also other ways you can tell search engines about pages that you want to be the canonical version:

  • Sitemap – Google automatically assumes that all URLs listed in Sitemap are main, canonical versions.
  • Redirect – Duplicate pages can transmit all page signals along with traffic to a single, canonical URL via 301 redirects.
  • Internal linking – Google can easily determine which pages are canonical if your site’s internal links point to them from duplicate pages.
  • HTTPS – Search engines like Google usually prefer pages that have a valid SSL certificate (unlike encryption – pages without HTTP) as canonical.

Canonical tags are the best practice

1. Use self-referencing canonical

Although it is not mandatory, It’s always a good idea to add a canonical tag to a page that points to you – Even if you don’t use canonical tags on the rest of the duplicate pages.

Using self-referencing rel=canonical Original, original pages give a clear signal to search engines like Google that they are the canonical version:

“I recommend doing this kind of self-referential rel = canonical because it really makes it clear to us which page you want to index or what should happen when indexing this URL.” (John Mueller).

2. Use absolute URL

Complete URLs in canonical tags can help you Avoid unintentional mistakes Or bad interpretation of canonical URLs By a search engine (as opposed to relative URLs).

Full URLs should also be included https, //, wwwAnd trailing slash (if possible).

Here’s an example of an absolute URL in a canonical tag:

<link rel="canonical" href="https://www.randomwebsite.com/randompage/" />

And here’s just an example of a relative URL:

<link rel="canonical" href="https://mangools.com/randompage/" />

3. Use short hand URLs

Search engines like Google can be sensitive to the top and bottom of the URL.

Using small cases in canonical URLs can help you keep consistency in the eyes of search engines and avoid duplication issues.

As a good practice, try to use lowercase letters in URLs on your server as well as apply them to canonical tags.

4. Canonicalize cross-domain duplicates

Canonical tags can also refer to your main pages from other domains – Not just from your website.

If you have duplicate content on the pages of a different website (such as redirected posts on some news sites), you should:

  • Use self-referencing canonical tags on your main page
  • Apply canonical tags to external pagesA reference to your original

What to avoid with canonical tags?

1. Multiple canonicals on 1 page

Focus on multiple canonical tags that may accidentally occur in a page’s HTML.

Although rare, Having more than 1 canonical tag on a page can be confusing for search engines and ignore this canonical signal.

Or as Google has officially said:

“In the case of multiple announcements of rel = canonical, Google will probably ignore all rel = canonical hints. Any valid rel = canonical offer may be lost. “

2. Avoid canonical in case of counterfeiting

Always make sure that the content of the duplicate pages and the original version of the page are identical or at least almost identical When applying canonical tags.

Applying canonical tags to completely different pages can confuse or completely ignore search engines:

Or as Martin Split explains:

“… if the content is completely different or different enough for algorithms that it is not a duplicate, then the canonical is meaningless.”

3. Canonical on pages with pages

Paginated pages contain fragmented content on different pages (such as the comments section of a website divided into “1”, “2”, “3” pages).

In this example, You should always use self-referencing canonical tags on each individual page – and do not specify the page “1” from the remaining pages:

“The main thing to avoid is, since this post is about canonicalization, the rel = canonical used on page 2 points to page 1. Page 2 is not equivalent to page 1, so would be a mistake like rel = canonical. “(John Mueller)

4. Do not block canonical through robots.txt

You should never block URLs with canonical tags from the robots.txt file.

Robots.txt will prevent Google from crawling duplicate pages – so it will be unable to see the canonical tags specified in the original version of the page.

In addition, Blocking URLs with canonical tags will prevent PageRank from migrating to your main version.

5. Do not use this canonical

Canonical tags should always be applied <head> Categories of your pages – Nowhere else in the HTML document.

Google will ignore your canonical tags <body> In the department or anywhere else.

6. Avoid canonical loops and chains

You should always try to use canonical tags that refer directly to the main page Avoid canonical loops (similar to redirection loops).

For example, using a canonical tag from page A to page B and then from page B to page C will create a canonical chain that can confuse search engines and waste their resources and time.

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