---
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</p>
   <p>For more information about MQTT, visit <a href="http://mqtt.org">mqtt.org</a>.</p>

   <section id="Download">
      <h2>Download</h2>
      <p>The latest version of the library can be downloaded from <a href="https://github.com/knolleary/pubsubclient/releases/latest">GitHub</a>.</p>
   </section>
   <section id="Documentation">
      <h2>Documentation</h2>
      <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="Hardware">
       <h2>Compatible Hardware</h2>
       <p>
           The library uses the Arduino Ethernet Client api for interacting with the
           underlying network hardware. This means it Just Works with a growing number of
           boards and shields, including:
       </p>
       <ul>
            <li>Arduino Ethernet</li>
            <li>Arduino Ethernet Shield</li>
            <li>Arduino YUN – use the included <code>YunClient</code> in place of <code>EthernetClient</code>, and
                be sure to do a <code>Bridge.begin()</code> first</li>
            <li>Arduino WiFi Shield - if you want to send packets greater than 90 bytes with this shield,
   enable the <a href="http://knolleary.github.io/pubsubclient/api.html#configoptions"><code>MQTT_MAX_TRANSFER_SIZE</code></code></a> option in <code>PubSubClient.h</code>.</li>
            <li>Sparkfun WiFly Shield – when used with <a href="https://github.com/dpslwk/WiFly">this library</a></li>
            <li>Intel Galileo/Edison</li>
            <li>ESP8266</li>
        </ul>
        <p>
            The library cannot currently be used with hardware based on the ENC28J60 chip –
            such as the Nanode or the Nuelectronics Ethernet Shield. For those, there is an
            <a href="https://github.com/njh/NanodeMQTT">alternative library</a> available.
        </p>
    </section>

    <section id="Author">
       <h2>Author</h2>
       <p>Nick O'Leary - <a href="https://twitter.com/knolleary">@knolleary</a></p>
    </section>
    <section id="License">
       <h2>License</h2>
       <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">
      <h2>Change History</h2>
      <p>The complete change history is available on <a href="https://github.com/knolleary/pubsubclient/commits/master">GitHub</a>.</p>
      <dl>
         <dt>2.0</dt>
         <dd>
            <ul>
               <li>Add (and default to) MQTT 3.1.1 support</li>
               <li>Fix PROGMEM handling for Intel Galileo/ESP8266</li>
               <li>Add overloaded constructors for convenience</li>
               <li>Add chainable setters for server/callback/client/stream</li>
               <li>Add state function to return connack return code</li>
            </ul>
         </dd>
         <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>