The Canonical URL plugin for WordPress that is designed to make it clear to search engines which URL it should consider canonical for a page when you might be using multiple URLs to reference it, for example for marketing purposes,
Suppose you have read my Twitter Analytics post, and you’ve started tagging all the URL’s you spread on Twitter with Google Analytics campaign variables. So at some point, a search engine would enter your site through this URL:http://yoast.com/twitter-analytics/?utm_source=twitter&utm_medium=twitter &utm_campaign=twitter
If it did, in “old times”, this would mean you’d have a duplicate content issue: the same content indexed under two different URL’s. An issue SEO’s have been trying to solve on web pages for ages, which sometimes created huge limitations. This is where the canonical tag, and thus this plugin, comes in. The plugin will add this code to the
<head>section of your page:<link rel="canonical" href="http://yoast.com/twitter/analytics/"/>
And now, the search engine will suddenly count the links it has seen to that campaign tagged URL, towards the canonical URL, and not index the campaign tagged URL anymore. Simple, yet effective.
According to the developer of the plugin, Google already supports the “rel=canonical” metadata, and Yahoo! and Live Search have said they will soon. Interesting.