If you're running a Web site, then the last thing you want is to
  have a broken link.  Broken links look bad, frustrate users, and
  confuse search engines.  Even when links aren't broken, you can have
  pages that contain bad HTML, or server-side programs that fail when
  you enter data into them.  If this is an important issue to you,  then you should take a look at Tarantula,
  a Rails plugin that executes a number of simple tasks against your
  Web site, producing a detailed report (in HTML, of course)
  describing the URLs that it crawled, and the responses it received
  from each URL.