By default, Magento uses the .html extension in all catalog based URL’s and quite often a site may launch using this default URL format. Most Magento store owners will be aware that from the Magento admin, you can easily remove the default .html extension from the URL’s (like the screenshot below) but once a store has already gone live and there are already thousands of the .html URL’s indexed in search engines or many backlinks pointing the .html URL’s, you should implement a global 301 redirect to handle the redirecting of all URL’s containing a .html extension to the counterpart without.

You can access the above with your Magento admin at System > Configuration >CATALOG > Catalog > Search Engine Optimizations and then the Product URL Suffix and Category URL Suffix will contain the .html extension that you can remove.

By removing the .html suffix, you can modify URL’s from the likes of:-

http://www.example.com/category/product.html

To the more friendlier / cleaner counterpart:-

http://www.example.com/category/product

So immediately after removing the .html extension suffix from the fields in the above screenshot, you must immediately ensure that all URL’s with .html 301 redirect to the version without by implementing a rule in your Magento root .htaccess like so:-

Find RewriteBase / in your .htaccess file and add the following directly below it:-

This rule may require to be implemented in different ways from store to store depending on the setup and any other rewrites it may have in place.