In a perfect world, duplicate content would not exist on the web and there would only be one version of every page. In the real world, duplicate content can exist in several locations and on multiple websites. To help manage issues stemming from repetitive content, the canonical link element was created, which is commonly referred to as the canonical tag.

Why does a canonical tag help with search engine optimization? They work by establishing the favored page version and sending signals, like links to the favored version. As a result, the canonical tag orders copied content which can arise from certain issues like:

  • Variations of www and non www
  • Default and index pages
  • HTTPS and HTTP
  • Alternate page or print copies

Most SEO companies know that canonical tags can be placed in the head area, but some may not realize they can also be used in the HTTP header as well. The most frequent use of these tags being used on pages is for setting a favored version when you also have a PDF copy online. Here is how they should look:

HTTP Section:

HTTP/1.1 200 OK

Link: <https://pageexample.com/>; rel=”canonical”

Header Section:

<link rel=”canonical” href=”https://pageexample.com/” />

In addition to being used on your website, canonical tags can also be used across different domains and is considered the standard method to use when syndicating content.

There are some cases where canonical tags are not correctly used, which works against your search engine optimization services. Here are the two most frequent misuses:

Do Mixed Signals Occur?

By default, a canonical tag is not directive. The version of your site page that is submitted to sitemaps should also be the canonical version, as having different URLs within your sitemap or internal page links can give mixed messages. If the pages are not closely enough related, your tag may be ignored by search engines.

Other issues can arise as well, such as if you copy a page and do not change the tag or accidentally leave a placeholder such as ‘replace me’ within your canonical tag. Always avoid relative path URLs with the tag to avoid errors and avoid using multiple, different, canonical tags on the same page – a surefire way for the search engines to ignore.

If mixed signals are being sent to a search engine, they will guess as to which the best URL is based on the sitemap, internal links, and the suggested canonicals. Google may also select a short URL over a lengthy one or give preference to a URL with HTTPS. In fact, under these circumstances, Google will always pick the HTTPS page except when the following errors occur:

  • The page contains a noindex robots meta tag
  • The canonical tag links to the HTTP page
  • Invalid SSL certificate on the page
  • The HTTP page is not roboted but the HTTPS page is

Used Instead of 301 Redirects

For those not advanced in SEO, it can appear at first glance that a canonical tag and 301 redirects do the same function. It’s true that they do not advise search engines to treat the multiple URLs or pages as a single page, but the 301 redirect is what sends all traffic to the specific URL, which is something that the canonical tag will not. If your website structure has changed, don’t make the mistake of using a canonical tag in place of a 301 redirect, which will also correct bookmarks.

When faced with having repetitive content, the relevance of your search engine results and how your pages ranks can be impacted, which can alter your site’s overall traffic. While the canonical tag is not a foolproof solution, they can improve your preferred pages visibility. On the other hand, if used incorrectly, you may be negatively affecting your overall rank. If deciding to use canonical tags, first create a strategy on where you need is- such as multiple URLs that all point to the same content and design a strategy on where and what pages to implement the tags on. Always make sure to double check and ensure that you are not accidentally hiding any pages that should be indexed or sending mixed signals to search engines.

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