Google Webmaster Tools is a no-charge web service by Google for webmasters. It allows webmasters to check indexing status and optimize their websites. It has tools that let the webmasters submit and check sitemaps, generate and check robots.txt files, list internal and external pages linking to the site, view statistics related to how Google crawls the site, disavow links, and more. Google WMT's is a must-have for any site looking to optimize.