Using the canonical link smartly

There’s a fairly obscure bit of code available for web pages which can improve your search engine performance noticeably if used well in certain situations. It’s called the ‘rel=canonical tag‘ or ‘canonical link’. You don’t have to know exactly how it works, or how to implement it (there are website designers for that), but it’s useful to know what it can do (because many website designers have no idea).

What the canonical link does is to specify the ‘preferred’ address of a web page. It allows a page to be accessible through various addresses (URLs) but only be seen as one page by search engines.

For example, one of our clients’ websites has a structure which lets the product pages be accessed via several routes, such as:

  • website/manufacturer/product
  • website/application/product
  • website/product-class/product

…etc.

Now, many sites do this, but with most, the product page has the same address, however you reach it. With this particular site, that’s not the case – the actual address changes, and search engines see the same content several times over as apparently different pages. While they’re clever enough to know there’s no deception going on, the arrangement can cause problems: the search engine is left to choose which one to show, and (far more significantly), the link benefits are diluted around the ‘different’ pages.

Other content management systems might put ‘query strings’ on the end of addresses, while referencing the same page. So these might all be seen as different by a search engine, when they’re not:

  • bluewidgetcompany.co.uk/product1
  • bluewidgetcompany.co.uk/product1?source=menu
  • bluewidgetcompany.co.uk/product1?campaign=adwords

In all these cases, if the page has a canonical link behind the scenes, the search engines will see things as you’d want them to.

Do you have canonical links in place on your site? It’s fairly easy to find out: take a look at the page source code and search for ‘canonical’. It’s possible that your site only has canonical links on pages where they’re specifically needed, but it’s more normal for sites to have them on every page.

What few people know is that canonical links can be used across sites. So if you run multiple websites, it’s quite legitimate to run the same article on them all, but with a canonical link on each pointing to the ‘master’ version. Also, as this excellent Moz.com article describes, “if a publication wants to re-post your content on their domain, ask for (a canonical link) instead of – or in addition to – a link back”. The article also points out that the feature is built into Medium.com, which is a very interesting option if you have any articles with fairly broad appeal.