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Duplicate content beware: When to use the canonical tag in SEO

It was lauded as the most important advancement in SEO nearly ten years ago, so how essential is canonicalisation today?


Although Google suggests that 25-30% of the web is duplicate content (and that’s okay, btw) it’s vital to at least begin to think about when to use the canonical tag on your website. Don't do this and you run the risk of having your high-conversion landing pages being indexed incorrectly which will ultimately affect traffic volumes.


What is the canonical tag?


Put simply, the canonical tag is a short line of code <link rel=“canonical”> which you can include as part of the HTML header on your web page. Look for it in the same section as the Title attribute and Meta Description tag. 


Will my website be penalised if I don’t use the canonical tag for my duplicate content?


In a word, no. Google’s very own webmaster blog cited this back all-the-way-back in 2008 – and today, nothing has changed.


So what happens instead?


If some of your website’s content is duplicated across multiple pages, Google makes an educated guess to where the original source for the content is located and pulls this through in the search results. However, this isn’t ideal.


Let’s use this example to illustrate how this works. Imagine this: you sell pink trainers on your website. The product page for these trainers can be found through the following URLs:






As far as you and your customer base are concerned, the same web page appears on either URL, so why should you be concerned?


Search engines are easily confused. Unless you apply the canonical tag to at least one of these URLs (citing that the one URL relates to the other) you run the risk of being indexed incorrectly, hampering your traffic volumes.


It would be good practice to ensure that all URLs which include search identifiers (such as “?category=trainers&color=pink”) contained a canonical tag at the top of the page to ensure that search engines know to assign all SEO-value to the original page (in this case, /shop/pink-trainers).


If you’re feeling extra efficient, you could even include a self-referential canonical tag on the original page. So, on http://trainerland/shop/pink-trainers, you would include this canonical tag at the top of the page:


<link rel=”canonical” href=“http://trainerland/shop/pink-trainers”?>


…which will force home the fact that this, and no other, is the original page for this content.  Simple, huh? Now go do it.


For more SEO advice and to find out how to apply canonical tags to your website, get in touch.