Canonical Tags Explained

Canonical Tags Explained

Webmasters use canonical tags to direct search engines to URLs they need to have indexed. When you use a canonical tag or a canonical link element, you indicate to a search engine that there is a master copy of a page in existence. This way, you will avoid duplicate content when similar content appears on more than one URL. With a canonical tag, you indicate which among two or more URLs is essential so that Google knows which one to index.

Using canonical tags correctly is, therefore, important to a website’s SEO as it shows which URLs need indexing.

What is a canonical tag?

The canonical tag is an HTML specification appearing in the source code of a website’s header area. The tag comes in handy for websites with duplicate content. If a canonical URL is correctly marked, the search engines will correctly index pages avoiding duplicate content. Duplicate content hurts the SEO of a website seeing that duplicated content does not provide any value to the user. Before using a canonical tag, you can use a duplicate content checker to detect the presence of duplicate content.

Canonical URL Examples

When adding canonical tags, Google recommends that absolute URLs are used – the URL has to include the protocol.

The examples below show two websites URLs with the same content:

https://www.website.com/example.htm

https://www.website.com/examplepage/?session_id=xyz.htm

The first URL is the standard resource, while the second URL is a session that online shops use to store user-related data such as items in the shopping cart. Given that the first URL is the standard resource and, therefore more critical, it should appear as the canonical version. A canonical tag, therefore, needs to be integrated into the head element of the second page to direct to the first page. By so doing, Google and other search engines will see that the first page is more important and should be crawled and indexed in search engine results pages.

When the canonical tag is added in the metadata of the second URL, it will appear as shown below:

<link rel=”canonical” href=”https://www.example.com/examplepage.htm”> />

When to Use Canonical Tags

Canonical tags apply when you have similar content in different URLs. There are a few cases when you can have similar content in different URLs, including:

• When the homepage is available from different URLs such as www.website.com, website.com, or www.website.com/index.html and so many more
• When pages are accessible without trailing slashes and with case sensitivity
• In the case of URL rewriting, the server can only pay attention to one ID and also accepts variants of an address
• When IDs (such as session IDs or product filters) are used, but they do not change the content
• Content appears on different versions including print version and PDF among others
• There are different HTTPS versions of a website
• A website is accessible under HTTP without SSL encryption
• There is additional content published on external websites

Best Practices for Canonical Tags

Pagination: During pagination of a website with rel= “next” and rel= “prev,” pages should indicate themselves via canonical or else a “view-all” page should exist where visitors can see all products in one page. If you are using rel= “next” and rel= “prev,” you do not have to use canonical tags, but you can instead add a robot tag to the meta element of paginated pages. This will exclude the subpages from indexing.

Hreflang: In cases where a website uses hreflang, URLs can either refer to themselves with a canonical tag or not use a tag at all. Using both hreflang and canonical tags sends conflicting signals to Google. The hreflang tag indicates the presence of another language version while the canonical tag makes the version indicated the original URL.

NoIndex and Canonical Tags: Webmasters use noindex tags to indicate to Google that a specific URL should not be indexed. If a canonical tag refers to a page that the webmaster says should not be indexed, Google will receive unclear signals since the canonical tag refers to an essential page that a webmaster needs to be indexed. As such, a webmaster needs to choose either a canonical tag or a noindex tag but not to use both.

Frequent errors with Canonical Tags

Canonical tags show Google which pages to crawl and index and which pages to ignore. If a canonical tag is incorrectly applied, individual pages of your website might be entirely ignored by Google. If Google happens to ignore relevant pages due to an error in the application of canonical tags, your traffic and sales might tank. Before you use canonical tags, you need to ensure that the contents are indeed the same.

Some of the common errors include:

• Combining “noindex,” “nofollow,” or “disallow” tags with canonical tags which send conflicting signals to search engines
• A canonical URL that responds with a 404 status code – a 404 error will confuse Google crawlers, and therefore a canonical URL need to be available at all times
• The canonical link element should only appear in the body of a document without being repeated in the metadata
• Specifying a relative path as a canonical link element – this might result in misinterpretation of the tag, making it lose its effect. As such, the link needs to appear as a complete URL in the canonical tag
• Ignoring the syntax – all characters need consideration when specifying the URL. Google stated in 2017 that using a secure HTTPS would be considered when ranking pages. Granted, a canonical tag should direct from an HTTP to an HTTPS and not vice versa.
• The canonical tag directs to the homepage of your website – this would indicate that there are duplicate pages on your website
• A canonical tag should not refer to another canonical page as this will create canonical chains or cross-references

Importance of Canonical Tags for SEO

Canonical tags play a large part when indexing pages on your website. When used, these tags indicate to search engines that there is a standard resource or a page that is more relevant than other pages. This way, the issue of duplicate content is resolved. The tags should be implemented correctly to avoid conflicting tags sending signals to search engines.