Canonical tags: why use them?

The canonical tag has been defined as an indication in the source code of your web page. In a few years, it has become the usual way of telling search engines which version of a page is the reference. Carrying out a content audit will thus allow you to identify the shortcomings of your site. The other reason is to assess the level of your editorial content marketing. The audit is carried out by checking the URLs or the backlinks of your site. Here are the reasons to add canonical tags to a website.

The canonical tag is an HTML tag placed in the head of a page. It tells the robots of search engines such as Google which URL is the reference one, called canonical, among several pages with identical or very similar content.

Canonical tags will allow you to avoid duplication, that is, the multiplication of identical content. Content that has been copied and pasted, whether accidentally or intentionally, is considered duplicate content. The canonical URL is therefore the solution to this duplicate content problem, which harms the rankings of your web page. Minor changes cannot make a page unique when search engines consider it a duplicate. So changing the title or the content of a text is not enough.

Duplication harms rankings, because search engines do not know which version to show. The canonical tag asks them to keep only one URL among the identical pages and to credit it with the signals of the other versions, such as inbound links. The origin of the problem may lie in the very design of the site, or in having an online shop whose products are available on several other sites.

To protect your site's content against theft by other internet users, or by robots programmed to steal content automatically, a canonical URL pointing to the page itself is a useful precaution: if a robot copies your page with its source code, the copied tag still designates your page as the original. It is not absolute protection, since the copier can remove the tag: in the event of blatant theft, a removal request is still necessary.

While the primary aim of canonical links is to protect you against duplicate content, they can also be used in other situations.

First, when you republish on your site content that has already appeared elsewhere, it is advisable to add a canonical tag pointing to the original page. The two pages then do not compete with each other in the results of search engines such as Google.

Next, on e-commerce sites, the same page is often reachable at several URLs: marketing campaign tracking parameters, sorting, filters. The content of the page, however, does not change. In this case, canonical tags point search engines to the reference URL, without parameters.

As for syndication, it increases the visibility of a product or service on the internet by having content republished by other sites. To keep the original page as the reference version, the site republishing the content can add a canonical tag pointing to it; Google, however, rather recommends preventing the copy from being indexed (noindex tag).

As a reminder, canonical tags are placed directly in the site's source code. There are several tips for checking a site's canonical tags.

You can, for example, use crawling software such as Screaming Frog, or Google Search Console, to obtain the list of URLs in use.

Next, extract the canonical URL declared by each page and compare it with the URL of the page. If they are identical, no change is needed. Otherwise, check that the canonical URL is accessible: it must not return an error code such as 404 or 500.

Finally, if the canonical URL is itself redirected (301 code), you must point directly to the destination URL.

You must first list the URLs that seem to offer identical content. Tools such as Dupli Checker will flag duplicate content for you.

You can then select a URL that you consider essential to how your site works, for example the one with the most links and the most traffic. Ideal, then, for good rankings.

The next step is to add a link tag with the rel="canonical" attribute, pointing to the chosen URL, on all the pages that have the same content. This tag goes in the head section of the page's HTML code.

To complete the process, use the URL Inspection tool in Google Search Console. Webmasters can check there which canonical URL Google has selected: it may choose a different one from the one declared.

Note that for a WordPress site, canonical tags are added through plugins. Yoast SEO, for example, automatically adds a canonical tag to every page and lets you change it. Other CMSs such as Joomla, Drupal or PrestaShop also offer modules to make adding canonical tags easier. These are very useful when you do not have access to the page's source code.

When setting up canonical URLs, mistakes can happen. The most common mistake is to place the URL in the wrong place on the page. For example, placing the URL in the body rather than in the head of the site.

The other mistake to avoid is pointing the canonical tag of a page with distinct content to another page, or to the wrong page: that page may then disappear from the search results.

Finally, you should always favour absolute URLs, that is, those preceded by http or https, rather than relative ones.

• Duplicate content
• Internal PageRank
• Semantic similarity
• Analysing content according to ranking