title: What HTTP response headers are required
body: <p>What HTTP response headers are required to be sent from server to the client?</p>
  
  <p>I working to optimize the HTTP response headers to minimize the HTTP response overhead. I know "overhead" is somewhat exaggerated, but I like a clean output.</p>
  
  <p>I see a lot of websites, which sends redundant cache headers.</p>
  
  <p>e.g.</p>
  
  <p>It is redundant to specify both <code>Expires</code> and <code>Cache-Control: max-age</code>, or to specify both <code>Last-Modified</code> and <code>ETag</code>.</p>
  
  <ul>
  <li><a href="http://code.google.com/intl/en/speed/page-speed/docs/caching.html#LeverageBrowserCaching" rel="noreferrer">Source</a></li>
  <li>HTTP/1.1: Header Field Definitions</li>
  </ul>