Today came the announcement that all of the major search engines are going to support a ‘canonical’ URL hint that will allow site owners to specify a single URL for content that may be replicated across many URLs (such as for categories etc.).

To make use of this in Rails applications, I’ve written a plugin that allows you to easily specify canonical URLs for your content. To install it as a gem, just add this to your environment.rb :

config.gem 'mbleigh-canonical-url', :source => 'http://gems.github.com', :lib => 'canonical_url' 1 config . gem 'mbleigh-canonical-url' , : source =& gt ; 'http://gems.github.com' , : lib =& gt ; 'canonical_url'

Using it is extremely simple; just add this to the <head> section of your layout:

<%= canonical_link_tag %> 1 & lt ; %= canonical_link_tag % & gt ;

And in your controllers, any time you want to specify a canonical URL you can do so like this:

class BlogController < ApplicationController def show @post = find_post # assume this is a standard blog post type record canonical_url blog_post_path(post.year, post.month, post.day, post.slug) end end 1 class BlogController & lt ; ApplicationController def show @ post = find_post # assume this is a standard blog post type record canonical_url blog_post_path(post.year, post.month, post.day, post.slug) end end

Now any time the show action is run, no matter how the routing came to be there, a single canonical URL will be shown in the header. If no canonical URL is specified in the controller (or through the canonical_link_tag helper directly) the helper will not output anything, making it completely harmless to add to any application.

The source for the plugin is available on GitHub. So go forth and canonize your applications!