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MQTT

MQTT is the main protocol for controlling Tasmota devices

After you have a working MQTT broker you need to configure Tasmota to communicate with it. If you have no knowledge of what MQTT is, you can learn about it from MQTT Essentials articles.

Configure MQTT~

If you flashed a precompiled .bin or didn't enter MQTT info in user_config_override.h before compiling you have to configure it on your device first.

Configure MQTT using WebUI~

Go to Configuration -> Configure Other and make sure "MQTT Enable" box is checked.
Once MQTT is enabled you need to set it up using Configuration -> Configure MQTT.

Tip

While here, you might as well change the Friendly Name into something more descriptive than generic "Tasmota".
This is a must for Home Assistant autodiscovery feature.

Enable MQTT Configure MQTT

For a basic setup you only need to set Host, User and Password but it is recommended to change Topic to avoid issues. Each device should have a unique Topic.

  • Host = your MQTT broker address or IP (mDNS is not available in the official Tasmota builds, means no .local domain!)
  • Port = your MQTT broker port (default port is set to 1883)
  • Client = device's unique identifier. In 99% of cases it's okay to leave it as is, however some Cloud-based MQTT brokers require a ClientID connected to your account.
  • User = username for authenticating on your MQTT broker
  • Password = password for authenticating on your MQTT broker
  • Topic = unique identifying topic for your device (e.g. hallswitch, kitchen-light). %topic% in wiki references to this. It is recommended to use a single word for the topic.
  • FullTopic = full topic definition. Modify it if you want to use multi-level topics for your devices, for example lights/%prefix%/%topic%/ or %prefix%/top_floor/bathroom/%topic%/ etc.

Configure MQTT using Backlog~

Using a serial connection or the WebUI Console you can issue (or even better, paste a premade) Backlog command for quick and easy MQTT setup.

Backlog mqtthost <mqtt_broker_address>; mqttport <mqtt_broker_port>; mqttuser <username>; mqttpassword <password>; topic <device_topic>

After a reboot all necessary MQTT settings are configured. Don't forget, you can use Backlog for all commands!

Commands over MQTT~

To send commands and view responses you'll need an MQTT client.

Commands over MQTT are issued to Tasmota by using cmnd/%topic%/<command> <parameter>. If there is no <parameter> (an empty MQTT message/payload), a query is sent for current status of the <command>.

Tip

If you are using mosquitto_pub, you can issue an empty payload using the -n command line option. If your MQTT client cannot issue an empty payload, you can use the single character ? instead.

Command flow~

The following example will go in depth on what happens when you send an MQTT command.

A device was flashed and configured with the FullTopic as default %prefix%/%topic%/ and the Topic set to tasmota_switch. We want to see the current status of the switch and change it.

By looking at the commands table we can learn about the POWER command and options associated with it.

Ask the device for status

cmnd/tasmota_switch/Power      // an empty message/payload sends a status query
     stat/tasmota_switch/RESULT  {"POWER":"OFF"}  
     stat/tasmota_switch/POWER  OFF

We can see that the switch (device's relay) is turned off.

Send a command to toggle the relay

cmnd/tasmota_switch/Power  "TOGGLE"
     // Power for relay 1 is toggled
     stat/tasmota_switch/RESULT  {"POWER":"ON"}  
     stat/tasmota_switch/POWER  ON

We've sent the toggle command and received confirmation that the switch is turned on.

Tip

By default, Tasmota replies to all commands through .../RESULT. This behavior can be changed using SetOption4, which makes the commands reply on the endpoint matching the command name, ex. cmnd/tasmota/PowerOnState will send a response on cmnd/tasmota/POWERONSTATE.

Examples~

In the following examples %topic% is tasmota, FullTopic is %prefix%/%topic%/, and prefixes are default cmnd/stat/tele:

  • The relay can be controlled with cmnd/tasmota/POWER on, cmnd/tasmota/POWER off or cmnd/tasmota/POWER toggle. Tasmota will send a MQTT status message like stat/tasmota/POWER ON.

  • Power state message can be sent with the retain flag set using PowerRetain 1.

  • Telemetry messages can also be sent with the retain flag using SensorRetain.

  • For Sonoff Dual or Sonoff 4CH the relays need to be addressed with cmnd/tasmota/POWER<x>, where {x} is the relay number from 1 to 2 (Sonoff Dual) or from 1 to 4 (Sonoff 4CH). cmnd/tasmota/POWER4 off turns off the 4th relay on a Sonoff 4CH.

  • MQTT topic can be changed with cmnd/tasmota/Topic tasmota1 which reboots Tasmota and changes the %topic% to tasmota1. From that point on MQTT commands should look like cmnd/tasmota1/POWER on.

  • The OTA firmware location can be made known to tasmota with cmnd/tasmota/OtaUrl http://thehackbox.org/tasmota/release/tasmota.bin. Reset to default with cmnd/tasmota/OtaUrl 1.

  • Upgrade OTA firmware from the OtaUrl server with cmnd/tasmota/Upgrade 1.

  • Show all status information with cmnd/tasmota/Status 0.

  • The button can send a MQTT message to the broker that in turn will switch the relay. To configure this you need to perform cmnd/tasmota/ButtonTopic tasmota where tasmota equals to Topic. The message can also be provided with the retain flag by cmnd/tasmota/ButtonRetain on.

  • Sonoff Pow (and any device with sensors) status can be requested manually with cmnd/tasmota/status 8. Additionally, Tasmota periodically sends telemetry every TelePeriod, which defaults to 300 seconds (5 minutes).

  • When a Sonoff Pow (and any device with power metering sensors) threshold like PowerLow has been met a message tele/tasmota/POWER_LOW ON will be sent. When the error is corrected a message tele/tasmota/POWER_LOW OFF will be sent.

While most MQTT commands will result in a message in JSON format the power status feedback will always be returned like stat/tasmota/POWER ON as well.

Telemetry data will be sent by prefix tele like tele/tasmota/SENSOR {"Time":"2017-02-16T10:13:52", "DS18B20":{"Temperature":20.6}}

MQTT Topic Definition~

FullTopic~

This is the MQTT topic used to communicate with Tasmota over MQTT. It is created using tokens placed within a user definable string (100 character limit). The tokens are substituted dynamically at run-time. Available substitution tokens are:

  • %prefix% = one of three prefixes as defined by commands Prefix1 (default = cmnd), Prefix2 (default = stat) and Prefix3 (default = tele).
  • %topic% = one of five topics as defined by commands Topic, GroupTopic, ButtonTopic, SwitchTopic and MqttClient.
  • %hostname% = the hostname of the device as defined through the web UI (default = %s-%04d) or via Hostname command.
  • %id% = MAC address of the device.

Tip

These substitution tokens will be used in examples across the documentation

If FullTopic does not contain the %topic% token, the device will not subscribe to GroupTopic and FallbackTopic.

Tip

The order of %prefix% and %topic% doesn't matter, unless you have enabled Auto-discovery for Home Assistant (SetOption19). Enabling this option re-formats the FullTopic to required order.

Using the tokens the following example topics can be made:

  • FullTopic %prefix%/%topic%/ default
  • FullTopic tasmota/%topic%/%prefix%/
  • FullTopic tasmota/bedroom/%topic%/%prefix%/
  • FullTopic penthouse/bedroom1/bathroom2/%topic%/%prefix%/
  • FullTopic %prefix%/home/cellar/%topic%/

%prefix%

Tasmota uses 3 prefixes for forming a FullTopic:

  • cmnd - prefix to issue commands; ask for status
  • stat - reports back status or configuration message
  • tele - reports telemetry info at specified intervals

Warning

To solve possible MQTT topic loops it is strongly suggested that you use the %prefix% token in all of your FullTopics. Status and telemetry do not need a prefix.

%topic%~

All MQTT status messages will be sent using the configurable %topic% which must be made unique by the user. It can be called bedroom but it could also be called XP-TS_10 as long as the user knows what it is and where to find it.

Default Topic is tasmota_XXXXXX where XXXXXX is unique and derives from the last 6 characters of the MAC address

The use of the %topic% token is mandatory in case you want to use ButtonTopic and/or SwitchTopic. It also provides for GroupTopic and Fallback Topic functionality.

Tip

Use %prefix% and %topic% tokens at all time within your FullTopic definition!

GroupTopic~

Having two devices with the same topic allowed for MQTT commands to be sent once to make the devices act in conjunction. That inspired a third topic called GroupTopic. Devices with the same GroupTopic will all listen to that GroupTopic and react to the same MQTT command sent to it. You can use this to take global actions like updating firmware on all devices or split up devices into different groups using a unique GroupTopic for each group.

Default GroupTopic is tasmotas

FallBack Topic~

Initially Tasmota had one MQTT configurable topic planned called Topic. It soon became apparent that when two devices come online with the same topic this would be a challenge, to say the least!

Tasmota then introduced a unique, non-configurable "FallBack Topic" that allows MQTT communication regardless of the configurable topic. This fallback topic is just what it is meant to be: a fallback topic in case of emergency!

By default the Fallback Topic is DVES_XXXXXX_fb where xxxxxx is derived from the last 6 charactes of the device's MAC address (excluding :). It might look something like this: DVES_3D5E26_fb. You can find out the DVES code by looking at Information page in the webUI or issuing Status 6:

12:36:17 MQT: stat/tasmota/STATUS6 = {"StatusMQT":{"MqttHost":"1.1.1.1","MqttPort":1883,"MqttClientMask":"DVES_%06X","MqttClient":"DVES_3D5E26","MqttUser":"tasmota","MqttCount":1,"MAX_PACKET_SIZE":1000,"KEEPALIVE":30}}

Retained MQTT Messages~

If MQTT is defined and PowerRetain is used the last state will be stored permanently in MQTT database.

Command Description
PowerRetain Show current MQTT power retain state.
0 / off = disable MQTT power retain on status update (default)
1 / on = enable MQTT power retain on status update

BUT, a message in your MQTT broker flagged as 'retained' will always override the PowerOnState.

This is usually the main cause for "ghost switching". Learn more in MQTT retained messages explained. Check out this tutorial for troubleshooting switch ghosting.

Clearing Retained Messages~

To check, if there is a retain flag set for the switch's power topic, monitor cmnd/+/power in a MQTT client (recommended MQTT.fx for Windows or Eclipse Mosquitto in linux).

You can use Tasmota Device Manager to clear all retained messages for selected device with a single click.

Tasmota Device Manager

or use the following tutorials/forum threads: