A client library for the Arduino Ethernet Shield that provides support for MQTT.
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Arduino Client for MQTT

This library provides a client for doing simple publish/subscribe messaging with a server that supports MQTT.

  • It can publish QoS 0/1/2 messages and subscribe at QoS 0 or QoS 1.
  • Can join session on connect without cleaning it (cleanSession=false). Which means that network issues (causing disconnects) are not a problem to receive the unread messages.
  • The maximum message size, including header, is 512 bytes by default. This is configurable via MQTT_MAX_PACKET_SIZE in PubSubClient.h.
  • The keepalive interval is set to 15 seconds by default. This is configurable via MQTT_KEEPALIVE in PubSubClient.h.
  • The client uses MQTT 3.1.1 by default. It can be changed to use MQTT 3.1 by changing value of MQTT_VERSION in PubSubClient.h.


The library comes with a number of example sketches. See File > Examples > PubSubClient within the Arduino application.

Compatible Hardware

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:

  • Arduino Ethernet
  • Arduino Ethernet Shield
  • Arduino YUN – use the included YunClient in place of EthernetClient, and be sure to do a Bridge.begin() first
  • Arduino WiFi Shield - if you want to send packets > 90 bytes with this shield, enable the MQTT_MAX_TRANSFER_SIZE define in PubSubClient.h.
  • Sparkfun WiFly Shield – library
  • TI CC3000 WiFi - library
  • Intel Galileo/Edison
  • ESP8266

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 alternative library available.


This code is released under the MIT License.