It was lauded as the most important advancement in SEO nearly ten years ago, so how essential is canonicalisation today?
What is the canonical tag?
The canonical tag helps you prevent duplicate content issues on your website by specifying the "preferred" version of the content on your website. If you have several similar versions of the same content you can pick the "canonical" page and let search engines know that is the version you want to show in search results.
How to Use The Canonical Tag
Imagine having multiple versions of a product page on your website. These pages have the exact same content on them, they're just replicated due to different product features changing the URL. You can't really remove them as they're part of how your chosen CMS lists the product variations. The URLs look something like this:
So how do search engines know which version to show in search results?
This is where the canonical tag comes into play.
To mark a page as the canonical version, you'll need to place a HTML element within the header section of your duplicate pages, and link back towards your preferred version.
For example, we want to mark the default trainer URL as the preferred version. To do that we would add the following canonical tags onto the duplicate versions of the pages:
<link rel="canonical" href="https://www.example.com/shoes/trainers" />
Picking the Right Page to Canonicalise
If you're stuck trying to figure out which URL to pick as the canonical version, you should always pick the version that you think would provide the most value to your users. If you can't see a distinction between the two, pick the URL that has built up the most SEO equity over time - if one of the URLs has several natural occurring backlinks, then by all means use that URL.
When to use a Canonical Tag
If you're stuck between choosing whether to redirect a page or to use a canonical you should always stick to redirecting if that is an option. Canonical tags are not a replacement for great site architecture and there are often better ways to handle duplicate content.
As with most things, incorrect implementation of canonical tags can end up being a disaster for your organic performance. So we always suggest checking with an SEO expert first.