Google Webmaster Tools is a no-charge web service by Google for webmasters. It allows webmasters to check indexing status and optimize visibility of their websites.
It has tools that let the webmasters:
- Submit and check a sitemap
- Check and set the crawl rate, and view statistics about how Googlebot accesses a particular site
- Generate and check a robots.txt file. It also helps to discover pages that are blocked in robots.txt by chance.
- List internal and external pages that link to the site
- See what keyword searches on Google led to the site being listed in the SERPs, and the click through rates of such listings
- View statistics about how Google indexes the site, and if it found any errors while doing it
- Set a preferred domain (e.g. prefer example.com over www.example.com or vice versa), which determines how the site URL is displayed in SERPs