---
title: User-Agent
slug: Web/HTTP/Headers/User-Agent
tags:
  - HTTP
  - NeedsTranslation
  - Reference
  - TopicStub
  - header
translation_of: Web/HTTP/Headers/User-Agent
---
<div>{{HTTPSidebar}}</div>

<p>The <strong>User-Agent</strong> request header contains a characteristic string that allows the network protocol peers to identify the application type, operating system, software vendor or software version of the requesting software user agent.</p>

<div class="note">
<p>Please read <a href="/en-US/docs/Web/HTTP/Browser_detection_using_the_user_agent">Browser detection using the user agent</a> and why serving different Web pages or services to different browsers is usually a bad idea.</p>
</div>

<table class="properties">
 <tbody>
  <tr>
   <th scope="row">Header type</th>
   <td>{{Glossary("Request 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">User-Agent: &lt;product&gt; / &lt;product-version&gt; &lt;comment&gt;

Common format for web browsers:

User-Agent: Mozilla/&lt;version&gt; (&lt;system-information&gt;) &lt;platform&gt; (&lt;platform-details&gt;) &lt;extensions&gt;
</pre>

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

<dl>
 <dt>&lt;product&gt;</dt>
 <dd>A product identifier</dd>
 <dt>&lt;product-version&gt;</dt>
 <dd>A version number of the product.</dd>
 <dt>&lt;comment&gt;</dt>
 <dd>Zero or more comments containing sub product information, for example.</dd>
</dl>

<h2 id="Firefox_UA_string">Firefox UA string</h2>

<p>For more details on Firefox and Gecko based user agent strings, see the <a href="/en-US/docs/Web/HTTP/Headers/User-Agent/Firefox">Firefox user agent string reference</a>. The UA string of Firefox itself is broken down into four components:</p>

<p><strong>Mozilla/5.0 (<em>platform</em>; rv:<em>geckoversion</em>) Gecko/<em>geckotrail</em> Firefox/<em>firefoxversion</em></strong></p>

<ul>
 <li><em><strong>Mozilla/5.0</strong></em> is the general token that says the browser is Mozilla compatible, and is common to almost every browser today.</li>
 <li><strong><em>platform</em></strong> describes the native platform the browser is running on (e.g. Windows, Mac, Linux or Android), and whether or not it's a mobile phone. Firefox OS phones simply say "Mobile"; the web is the platform. Note that <strong><em>platform</em></strong> can consist of multiple "; "-separated tokens. See below for further details and examples.</li>
 <li><strong>rv:<em>geckoversion</em></strong> indicates the release version of Gecko (such as <em>"17.0"</em>). In recent browsers, <strong><em>geckoversion</em></strong> is the same as <strong><em>firefoxversion</em></strong>.</li>
 <li><strong><em>Gecko/geckotrail</em></strong> indicates that the browser is based on Gecko.</li>
 <li>On Desktop, <em><strong>geckotrail</strong></em> is the fixed string "20100101"</li>
 <li><em><strong>Firefox/firefoxversion</strong></em> indicates the browser is Firefox, and provides the version (such as "<em>17.0"</em>).</li>
</ul>

<h3 id="Examples">Examples</h3>

<pre>Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:47.0) Gecko/20100101 Firefox/47.0
Mozilla/5.0 (Macintosh; Intel Mac OS X <em>x.y</em>; rv:42.0) Gecko/20100101 Firefox/42.0
</pre>

<h2 id="Chrome_UA_string">Chrome UA string</h2>

<p>The Chrome (or Chromium/blink-based engines) user agent string is similar to the Firefox format. For compatibility, it adds strings like "KHTML, like Gecko" and "Safari".</p>

<h3 id="Examples_2">Examples</h3>

<pre>Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.103 Safari/537.36</pre>

<h2 id="Opera_UA_string">Opera UA string</h2>

<p>The Opera browser is also based on the blink engine, which is why it almost looks the same, but adds "OPR/&lt;version&gt;".</p>

<h3 id="Examples_3">Examples</h3>

<pre>Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.106 Safari/537.36 OPR/38.0.2220.41</pre>

<h2 id="Safari_UA_string">Safari UA string</h2>

<p>In this example, the user agent string is mobile safari version. It contains the word "Mobile".</p>

<h3 id="Examples_4">Examples</h3>

<pre>Mozilla/5.0 (iPhone; CPU iPhone OS 10_3_1 like Mac OS X) AppleWebKit/603.1.30 (KHTML, like Gecko) Version/10.0 Mobile/14E304 Safari/602.1</pre>

<h2 id="Internet_Explorer_UA_string">Internet Explorer UA string</h2>

<h3 id="Examples_5">Examples</h3>

<pre>Mozilla/5.0 (compatible; MSIE 9.0; Windows Phone OS 7.5; Trident/5.0; IEMobile/9.0)</pre>

<h2 id="Crawler_and_bot_UA_strings">Crawler and bot UA strings</h2>

<h3 id="Examples_6">Examples</h3>

<pre>Googlebot/2.1 (+http://www.google.com/bot.html)</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", "User-Agent", "5.5.3")}}</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">The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out <a href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a> and send us a pull request.</p>

<p>{{Compat("http.headers.User-Agent")}}</p>

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

<ul>
 <li><a href="https://hacks.mozilla.org/2013/09/user-agent-detection-history-and-checklist/">User-Agent detection, history and checklist</a></li>
 <li><a href="/en-US/docs/Web/HTTP/Headers/User-Agent/Firefox">Firefox user agent string reference</a></li>
 <li>
  <p><a href="/en-US/docs/Web/HTTP/Browser_detection_using_the_user_agent">Browser detection using the user agent</a></p>
 </li>
</ul>