Improve SEO with Canonical Attribute
Although Google doesn’t directly penalize you for duplicate content, having more than one version can often split up the reputation of that content between URLs. Using the canonical attribute you can specify your preferred URL.
URL Parameters
www.websites.com/index.php?category=sample is not the same as www.website.com/index.php in Google’s eyes. The extra parameters could be something simple as sorting a table or how to organize the info on the page. It is still the same content just displayed differently. Unfortunately someone might share the URL with the parameters. This can hurt that reputation for that page. It will split amongst two different URLs.
Canonical Fix
If we wanted http://www.websites.com/index.php to be our preferred URL we simply add this to index.php:
This way if there is any additional parameters added to the URL Google knows to use your preferred URL instead.
www. and non-www.
Unfortunately this doesn’t solve the problem if your website uses both www.websites.com v.s. websites.com. What you have to do here is pick which one you want to use. Then just 301 redirect the other one to the one you would like.
Related Links
To see Googles take on this visit Google’s Blog
