The Free webmaster tools by Google are the useful tools that will help you, or your webmaster to make your site more Google-friendly. The webmaster tools will help you see Google’s view of your site, diagnose problems, and share information with Google in order to improve your site’s visibility in Google’s search results.

Google Webmaster Tools will help you know—

How can you let Google know about all the pages on your site?
What search-queries will bring you site the most traffic?
Why is your site being returned for particular keywords?
What page according to Google are the most important one on your site?