Google, Yahoo, and MSN have apparently agreed on a tag to use to specify the "canonical" URL for a particular page, to avoid multiple versions of the URL being indexed, creating duplicate content issues:
This is great, but how do I find out if I HAVE duplicate content issues that I might need to remedy with this? I would have to put the tag in the head of every page involved, and it's different for every page....
I think I've sorted all my accidental non-canon problems out with 302s and 301s, etc, but I'm not sure if I should have my explicit mirror sites mark the 'main' site content as canonical. Those geographic mirrors are there for a reason...
I'm seeing these "Google ads new tag" all over the web.
There is no new tag! The tag is "link", the attribute is "rel". We're talking about a new value for the "rel" attribute.
A good use IMO is marking your printer friendly pages. But I don't know if the Search engines will think it's still a canonical page with all the navigation/ads stripped from the page. You can't typically 301 redirect these as they have a purpose but still are duplicate content.
For me this 301 redirects non-www to www
and any index to it's directory root & adds the / to the end of .com
I just took back a site I sold a little over a year ago due to non-payment, and the webmaster had deleted the .htaccess so he could do some redirects via a graphical interface, and it took away all the redirects I had done. Now the site is indexed with all kinds of canonical problems, including duplicate problems with http & https pages that I also resolved with another bit in .htaccess. I will have to wait until the search engines re-index the whole site, and finally drop all the canonical issue pages and list the pages the way I want.