Robots.txt file is a special text file that is always located in your Web server's root directory. Robots.txt file contains restrictions for Web Spiders, telling them where they have permission to search. A Robots.txt is like defining rules for search engine spiders (robots) what to follow and what not to. It should be noted that Web Robots are not required to respect Robots.txt files, but most well written Web Spiders follow the rules you define.