Revision 1088717 of Content-Encoding

<div>{{HTTPSidebar}}</div>

<p>The <strong><code>Content-Encoding</code></strong> header indicates which algorithm is used for the message.</p>

<table class="properties">
 <tbody>
  <tr>
   <th scope="row">Header type</th>
   <td>{{Glossary("Response header")}}</td>
  </tr>
  <tr>
   <th scope="row">{{Glossary("Forbidden header name")}}</th>
   <td>no</td>
  </tr>
 </tbody>
</table>

<h2 id="Syntax">Syntax</h2>

<pre class="syntaxbox">
Content-Encoding: gzip
Content-Encoding: compress
Content-Encoding: deflate
Content-Encoding: identity
Content-Encoding: br
</pre>

<h2 id="Directives">Directives</h2>

<dl>
 <dt><code>gzip</code></dt>
 <dd>A format using the <a class="external" href="http://en.wikipedia.org/wiki/LZ77_and_LZ78#LZ77">Lempel-Ziv coding</a> (LZ77), with a 32-bit CRC. This is originally the format of the UNIX <em>gzip</em> program. The HTTP/1.1 standard also recommends that the servers supporting this content-encoding should recognize <code>x-gzip</code> as an alias, for compatibility purposes.</dd>
 <dt><code>compress</code></dt>
 <dd>A format using the <a class="external" href="http://en.wikipedia.org/wiki/LZW">Lempel-Ziv-Welch</a> (LZW) algorithm. The value name was taken from the UNIX <em>compress</em> program, which implemented this algorithm.<br />
 Like the compress program, which has disappeared from most UNIX distributions, this content-encoding is used by almost no browsers today, partly because of a patent issue (which expired in 2003).</dd>
 <dt><code>deflate</code></dt>
 <dd>Using the <a class="external" href="http://en.wikipedia.org/wiki/Zlib">zlib</a> structure (defined in <a class="external" href="http://tools.ietf.org/html/rfc1950">RFC 1950</a>), with the <a class="external" href="http://en.wikipedia.org/wiki/DEFLATE"><em>deflate</em></a> compression algorithm (defined in <a class="external" href="http://tools.ietf.org/html/rfc1952">RFC 1951</a>).</dd>
 <dt><code>identity</code></dt>
 <dd>Indicates the identity function (i.e. no compression, nor modification). This token, except if explicitly specified, is always deemed acceptable.</dd>
 <dt>br</dt>
 <dd>A format using the <a href="https://en.wikipedia.org/wiki/Brotli">Brotli</a> algorithm</dd>
</dl>

<h2 id="Examples">Examples</h2>

<h3 id="Preventing_caching">Compressing with gzip</h3>

<pre>
Content-Encoding: gzip</pre>

<h2 id="Specifications">Specifications</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Title</th>
  </tr>
  <tr>
   <td>{{RFC("7231", "Content-Encoding", "3.1.2.2")}}</td>
   <td>Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</td>
  </tr>
 </tbody>
</table>

<h2 id="Browser_compatibility">Browser compatibility</h2>

<p class="hidden">To contribute to this compatibility data, please write a pull request against this file: <a href="https://github.com/mdn/browser-compat-data/blob/master/http/headers.json">https://github.com/mdn/browser-compat-data/blob/master/http/headers.json</a>.</p>

<p>{{Compat}}</p>

<h2 id="See_also">See also</h2>

<ul>
 <li>{{HTTPHeader("Accept-Encoding")}}</li>
 <li>{{HTTPHeader("Transfer-Encoding")}}</li>
</ul>