Here we will discuss the techniques and methods for detecting and correcting canonical tag errors. As a reminder on these tags’ definition, as well as their role, don’t hesitate to read our article on this topic.
The first step is to locate the canonical tags on your website. During an audit, a crawler is used to locate all the URLs and their tags. It’s also possible to use a plugin. However, the plugin will only show the tag located on the page we’re visiting. You need a crawler for a full list.
Case #1: missing tags
Firstly we check pages that do not have a canonical tag :
If there is none: so much the better, there is nothing to do
If there are any: locate the number and type of page(s) concerned. If these are pages to be deindexed (shopping cart, etc.), check that they are deindexed or proceed to deindex them. Otherwise, you must add a canonical "self-referencing" tag. In other words, this tag points to the page in question, to indicate to Google that it’s the original page and to avoid duplicate content.
Canonical self-referencing tag:
if my website is:
my tag will be:
<link rel="canonical" href="https://mywebsite.com/" />
Case #2: present tags
Logically, the website’s crawl should allow us to see the following equation:
The website’s total pages = Nb missing canonicals + Nb implemented canonicals
With Nb implemented canonicals = Nb self-referencing canonicals + Nb "referencing other" canonicals
==> We will therefore be interested in the implemented canonical tags to analyze their type.
Case 2.1: as many implemented canonical tags as self-referencing canonical tags
This means that all the tags on your website point to the page itself: this is the tag’s most frequent use.
There should not be anything to do, unless you find yourself in one of the cases justifying to point the canonical to another page. For example, if a website uses an article already published elsewhere, for example to give visibility to partner bloggers, they need to add a canonical tag pointing to the original page.
Case 2.2: fewer self-referencing canonicals than the total of implemented canonicals
This means that you’ve got canonicals tags which point to other pages and not to "themselves".
If it’s because of your website’s pagination: if you’ve got paginated pages, it’s very common that all the pages after the first one have a canonical pointing towards page 1. In this case, we advise you to modify this operation by putting a canonical self-referencing tag. So, Google can explore and view all the pages’ content.
Otherwise: are these duplicate pages? If they are duplicate pages that need to exist (example of content syndication’s case 2.1 above), then keep the canonical. If, on the other hand, these are pages that should not exist in duplicate, such as URL changes for example, then it’s not the canonical tag that must be set up, but a 301 redirection from the “old” URL to the new one.
Indeed, the 301 redirection makes it possible to direct the old page’s traffic to the new one, and to control your website’s internal linking, while avoiding to create identical pages that are not needed for the user.
Now you are a pro in canonical tags’ audit!
Find out more:
The URL or Canonical Tag: Definition and usefulness in SEO
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