title: Which status code should I use for failed validations or invalid duplicates?
body: <p>I am building an application with a REST-based API and have come to the point where I am specifying status codes for each requests.</p>
  <p>What status code should i send for requests failing validation or where a request is trying to add a duplicate in my database?</p>
  <p>I've looked through <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html" rel="noreferrer">http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html</a> but none of them seems right.</p>
  <p>Is there a common practice when sending status codes?</p>