---
layout: default
title: Arduino Client for MQTT
---
   <p>This library provides a client for doing simple publish/subscribe messaging with a server that supports MQTT v3.</p>
   <p>For more information about MQTT, visit <a href="http://mqtt.org">mqtt.org</a>.</p>

   <section id="Download">
      <h3>Download</h3>
      <p>The latest version of the library can be downloaded from <a href="https://github.com/knolleary/pubsubclient/tags">GitHub</a>.</p>
   </section>
   <section id="Documentation">
      <h3>Documentation</h3>
      <p>The library comes with a number of example sketches. See <code>File &gt; Examples &gt; PubSubClient</code> within the Arduino application.</p>
      <p>Full <a href="api.html">API Documentation</a></p>
   </section>
   <section id="License">
      <h3>License</h3>
      <p>This library is released under the <a href="http://www.opensource.org/licenses/mit-license.php">MIT License</a>.</p>
   </section>
   <section id="ChangeHistory">
      <h3>Change History</h3>
      <p>The complete change history is available on <a href="https://github.com/knolleary/pubsubclient/commits/master">GitHub</a>.</p>
      <dl>
         <dt>1.9</dt>
         <dd>
            <ul>
               <li>Do not split MQTT packets over multiple calls to <code>_client->write()</code></li>
               <li><b><i>API change</i></b>: All constructors now require an instance of Client to be passed in.</li>
               <li>Fixed example to match 1.8 api changes - dpslwk</li>
               <li>Added username/password support - WilHall</li>
               <li>Added <code>publish_P</code> - publishes messages from <code>PROGMEM</code> - jobytaffey</li>
            </ul>
         </dd>
         <dt>1.8</dt>
         <dd>
            <ul>
               <li>KeepAlive interval is configurable in <code>PubSubClient.h</code></li>
               <li>Maximum packet size is configurable in <code>PubSubClient.h</code></li>
               <li><b><i>API change</i></b>: Return <code>boolean</code> rather than <code>int</code> from various functions</li>
               <li><b><i>API change</i></b>: Length parameter in message callback changed from <code>int</code> to <code>unsigned int</code>
               <li>Various internal tidy-ups around types</li>
               <li>Able to specify server address by DNS name</li>
            </ul>
         </dd>
         <dt>1.7</dt>
         <dd>
            <ul>
               <li>Improved keepalive handling</li>
               <li>Updated to the Arduino-1.0 API</li>
            </ul>
         </dd>
         <dt>1.6</dt>
         <dd>
            <ul>
               <li>Added ability to publish retained messages</li>
            </ul>
         </dd>
         <dt>1.5</dt>
         <dd>
            <ul>
               <li>Added default constructor</li>
               <li>Fixed compile error when used with arduino-0021 or later</li>
            </ul>
         </dd>
         <dt>1.4</dt>
         <dd>
            <ul>
               <li>Fixed connection lost handling</li>
            </ul>
         </dd>
         <dt>1.3</dt>
         <dd>
            <ul>
               <li>Fixed packet reading bug</li>
            </ul>
         </dd>
         <dt>1.2</dt>
         <dd>
            <ul>
               <li>Fixed compile error when used with arduino-0016 or later</li>
            </ul>
         </dd>
         <dt>1.1</dt>
         <dd>
            <ul>
               <li>Reduced size of library</li>
               <li>Added support for Will messages</li?
               <li>Clarified licensing &#8211; see LICENSE.txt</li>
            </ul>
         </dd>
         <dt>1.0</dt>
         <dd>
            <ul>
               <li>Only Quality of Service (QOS) 0 messaging is supported</li>
               <li>The maximum message size, including header, is 128 bytes</li>
               <li>The keepalive interval is set to 30 seconds</li>
               <li>No support for Will messages</li>
            </ul>
         </dd>
      </dl>
   </section>