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The Canonical Tag: Handy Tool Or A Waste of Time?
The canonical tag was introduced way back in 2009, which is the equivalent of about 25 years in SEO terms. It still remains something of a bone of contention among SEOs, however, regarding its effectiveness and reliability.
The canonical tag (or ‘rel=canonical’) was born out of the need for SEOs to be able to redirect the linking power of a number different URLs with identical content. An example of this could be the following three URLS:
Having a single page of content with three different URLs presents a vast array of issues, not least when it comes to inbound links. Above, I’ve listed three hypothetical URLs for a single product page selling fish (I’m not sure if the folks at site.co.uk actually sell fish, by the way). Say someone decided that they really enjoyed this particular type of fish and wanted to tell everyone about it, so linked to the product page using the top URL. Then someone else – perhaps another fish lover – linked to the same fish product using the second URL. And then another fan of chicken of the sea decided to use the bottom URL. What would happen?
In short, not a great deal – the internet won’t explode or anything like that. It would affect our authority built through links however. Each of those links points to a different version of the same page, meaning that each of those pages gets one ‘vote’ and so the value of those links is divided. If all the links pointed to the first URL, we’d have three ‘votes’ for that page and thus more ranking power would be passed to that page.
The canonical tag is a quick fix to this problem. By entering the ‘rel=canonical’ tag into the header of your page along with the URL of the version of the page you want search engine bots to index, you essentially suggest to Google, Bing and Yahoo (yeah, alright…) to send all of the link love (for that is what it has been christened) to that version of the page. Here’s what that looks like in practice:
Image credit: SEOmoz
Rel=canonical provides a good solution for sites that have been migrated from one CMS to another (say from Drupal to Magento Ecommerce) and thus may have multiple URLs for a homepage, or for ecommerce sites with lots of versions of what is essentially the same product (so different colours and sizes of a t-shirt). It can also be used for URLs altered by navigation and referral data – so a product that can be reached through more than one category on an ecommerce site for example.
So that’s that then – all of our canonical issues solved. Well, not quite. If you have an excellent memory and/or actually read and digest every last word I write, you might recall I used the words ‘quick fix’ and ‘suggest’ about two paragraphs ago.
Opinion on rel=canonical, depending on who you ask, ranges from useful resource to potentially site-destroying waste of time. It could also be argued that it provides less of a solution to the problem of duplicate URLs than other methods.
For an example of how the canonical tag can destroy your site, take a look at this post by Dr. Pete. For those who can’t be bothered to click through, he basically took a canonical tag-shaped hatchet to his beloved site in the name of science and placed a canonical tag directed to his own page on every page on his site. Cue deindexing galore.
There’s also the issue of how the different search engines deal with rel=canonical. Google’s official line is that it’s a suggestion rather an order, meaning their bots can choose to ignore it, although in most cases the tag is observed. Bing takes much the same stance, although it has been suggested that Bing’s bunch of feckless bots choose to ignore your pleasant suggestion more often.
When Is Rel=Canonical Useful?
So what is the point of rel=canonical? Well, it’s extremely useful if you don’t happen to have a web development team to hand. While we’re lucky enough at Fluid to have a squadron (brood? cult?) of developers upstairs ready and waiting to implement all of our 301 redirects, the canonical tag provides an easy way to sort out duplicate content issues for those without the technical expertise required for 301 redirects.
They can also provide a less drastic solution to redirects for URLs you don’t necessarily want to lose entirely (so variations of a product, for example) but for which you want linking power to go to a single page. This could also be achieved through the meta robots tag and ‘nofollow’ but you would lose some of the ranking power passed by the links.
On the whole, however, rel=canonical should be considered a last resort rather than the first solution. Building a site that doesn’t generate duplicate URLs and sorting out your site structure should probably be your first solution, followed by 301 redirects and then the canonical tag. That said, it’s a useful tool to have lying about so don’t discount it completely!