Google now supports cross domain canonical tag
Back in February 2009 – Google, Yahoo! and Microsoft all announced that their search engine platforms would support a new type of tag that would inform search engine spiders of the ‘canonical’ page when there are several available. This tag could be used only internally or on a subdomain of that URL. Last week Google announced on their blog that the tag is supported across multiple domains. This will help webmasters who (for whatever reason) do not have server side control over their websites, whilst allowing the source domain to take precedent over any duplicate URLs.
I’m sure you’re all aware of the tag setup, if not you’ll find an example below:
<head>
...
<link rel="canonical" href="http://www.example.com/example-page.html" />
</head>
This informs the search engine robots of the page that is deemed to be the ‘canonical’ one if there are many available. So for example – say you’re signed up to an affiliate programme where they use a tracking parameter like so:
http://www.example.com/example-page.php?affiliate=blueberry
You don’t want to have both the main page and the ‘blueberry’ page indexed, resulting in a canonicalization issue. Therefore if you place the following canonical tag on both pages, the search engine robots are aware that all the link juice will attributed to the page specified in the href attribute:
<head>
...
<link rel="canonical" href="http://www.example.com/example-page.php" />
</head>
From tests that have been rolled out to client websites, the tag works a treat for this type of setup. 301 redirects vs. the canonical tag is a separate debate as the canonical tag will never make the 301 redirect process redundant. However, this is for internal pages rather than the new development, which targets external pages. We are still waiting to hear from Bing and Yahoo! on how their platforms will support external version – however it is clear that Bing might not be ready for a few more months yet.
So what benefits can we get from being able to use the canonical tag cross domain. Well for starters, bloggers using Google Blogspot that wish to move to a more ‘snazzy’ URL can replicate all of their older posts on their new domain, whilst of course adding the canonical tag with the URL of the post on the new URL. Simple and effective considering there isn’t a way to place server side redirects using this type of platform.
From a downside, there is a of course potential for blackhat SEOs to manipulate the tag. Then we can’t ignore the possibility of cloaking as it is fully possible for a webmaster to make a legitimate informative website that accumulates a vast amount of links and place a canonical tag to either an identical/similar website that is styled differently. However, I do believe that the positives out weigh the negatives here. Blackhat and unethical SEOs will always exist, however as search advances even further, these techniques will become redundant.
I have found a great example of where this tag could be used to compact duplicate content from other webmasters using your content. We all know how great the BBC website is for providing us with upto date relevant content from an authoritative source. As a football fan i’m always keen on finding out the latest news in the Premier League. Looking at the rankings over the past six months for the keyword term ‘Manchester United News’ you will see the inclusion of an identical site to the BBC – http://www.simonbaker.me/sport1/hi/football/teams/m/man_utd/default.stm. Take a look at the identical keyword density values:
Now have a look at the positioning over time of both URLs:
The dates are from 1st June 2009 to the 20th December 2009 in Google UK. You can see the inclusion of www.simonbaker.me throughout the month of November – however if the BBC had of included the following tag (and of course it was supported at the time!), the website would never have ranked for that keyword term:
<head>
...
<link rel="canonical" href="http://news.bbc.co.uk/sport1/hi/football/teams/m/man_utd/default.stm" />
</head>
This of course can work for webmasters who do not have control over server side redirects, or indeed if there were a situation where by website A was the chosen URL, however website B still needed to be accessible to the public without redirecting to website A. To conclude, the use of the tag for SEOs has many benefits when used correctly. The tag isn’t a replacement for a 301 redirect – however, it can make an SEOs life easier if the technical team are happier to setup this tag rather than a number of redirects.