Canonical tags (aka canonical URLs)
“A canonical URL is the URL of the best representative page from a group of duplicate pages” – Support.Google
There are times you may have two or more pages with similar content. Maybe you offer 12 variations of the same widget. Or perhaps your widget can be used for different purposes and has a page for each purpose; you’ll have two pages with duplicate content and the same item number. You may even have two websites where you sell the same item. Good on you: you’re cross-listing with the best of ‘em.
The links below are for two pages that have almost the same content.
SEO and duplicative copy
The asterisk here is that duplicate content can be bad for SEO. Google may think that you’re nefariously copying someone else’s site, and they’ll raise an eyebrow at you. Or they rank the pages, prioritizing one over the other. It might be fine to let them make that choice, but why not tell them which page is more important to you? This is why we use canonical tags.
Canonical tags vs redirects
A canonical tag is different from a redirect. You know how sometimes you’ll type in a URL, and you’ll be taken to a different page entirely, maybe even on a different website? That’s a redirect; you can’t actually get to the page you want, because the website owner automatically sends you to the second page.
A canonical tag is something you’ll never notice when browsing. It’s strictly for search engines; it tells them which page is the most important to you.
Yoast and Canonical tags
In my websites, I tag pages canonically in the Yoast panel. Under the SEO Tab, scroll down to Advanced > Canonical URL and the URL gets pasted there.
For my example above, I would choose which page is my root content and list that in the other page’s Yoast panel. I’ve now told search engines two things. Firstly, it can think of those two pages as one, and secondly, which page should get traffic.
Self-referencing canonical links
Even if you have a page that has unique content, it is smart to add a canonical link; in this case, the page points to itself. In various circumstances, third parties may add gibberish to the end of your page’s URL. By adding a self-pointing canonical link to your page or post, you know that search engines will point people to your original page regardless of what other people are up to.
Can you post without canonical links? Yep. But when I’m creating a new post, it adds 10 seconds to my procedure, so why wouldn’t I?