In 2009 we saw the introduction of the canonical tag. Announced by Google back in February the canonical tag was jointly introduced by Google, Yahoo and Microsoft with a sole purpose of providing an easier way of preventing the search engines form indexing duplicate content on a single website.
Over the year there has been scrutiny over the effectiveness of the tag including how the search engines handle it. It would appear that Google began to use the tag appropriately however the other search engines were still having problems with it. This led many to conclude that 301 redirects are and will continue to be the preferred option when handling duplicate content – and rightly so.
Yesterday Google announced that they are now supporting the canonical tag for handling duplicate content across different domains. Google also included the following graphic to make it a bit clearer:
This is a welcome decision as some sites can make it difficult to work around duplicate issues particularly when some hosts do not allow you to use 301 redirects.
Moreover I think it is a good addition when you only want to redirect the search engines to a different site rather then the user which can be the case with tracking parameters etc. appended to URLs.
The post from Google also gives some Q & A’s to help you understand when is best to use it so well worth a look if you’re still unsure about it.