Canonical tags, also known as rel=canonical, are HTML tags that are used to address duplicate content issues on a website. These tags are added to the head section of the HTML code of a web page to indicate the original version of a page when duplicate content exists on multiple pages.
The canonical tag is used to tell search engines which URL is the preferred version of a web page when there are multiple versions available.
Mistake #1
One of the most common mistakes I see is adding canonical tags to pages in a paginated series that point back to the first page. This is incorrect usage of canonical tags as these pages have different content.
It will also result in all of the content on page 2 and beyond not being indexed at all.
When it doesn’t get indexed, that means Google won’t see the internal links on the paginated pages pointing to the posts. This can cause additional indexing issues as well as weakening a site’s internal link structure.
Mistake #2
Absolute URLs mistakenly written as relative URLs.
I have found a lot of web designers and SEOs are not aware of this one. When https://domainname.com is missing from a <link> tag, it is assumed.
For example,
<link rel=”canonical” href=”domain.com/templates/journals” />
vs
<link rel=”canonical” href=”https://domain.com/templates/journals” />
or
<link rel=”canonical” href=”/templates/journals” />
In the first one, it is implied that the desired canonical is actually https://domain.com/domain.com/templates/journals.
The other two, correctly identify the proper URL with either an absolute or relative URL.
Mistake #3
Multiple rel-canonical tags. Happens a lot with SEO plugins creating additional tags.
The problem with having multiple canonical tags on one page is you cannot be sure which one Google is recognizing as the preferred tag.
