MQTT Discovery


The discovery of MQTT devices will enable one to use MQTT devices with only minimal configuration effort on the side of Home Assistant. The configuration is done on the device itself and the topic used by the device. Similar to the HTTP binary sensor and the HTTP sensor. To prevent multiple identical entries if a device reconnects, a unique identifier is necessary. Two parts are required on the device side: The configuration topic which contains the necessary device type and unique identifier, and the remaining device configuration without the device type.

Supported by MQTT discovery:

Configuration

MQTT discovery is enabled by default, but can be disabled. To do this, click on “Configure” in the integration page in the UI, then “Re-configure MQTT” and then “Next”.

Advanced discovery configuration

It’s possible to configure the prefix of the discovery topic through configuration.yaml.

Configuration Variables

discovery_prefix string (Optional, default: homeassistant)

The prefix for the discovery topic.

Discovery messages

Discovery topic

The discovery topic needs to follow a specific format:

<discovery_prefix>/<component>/[<node_id>/]<object_id>/config
  • <component>: One of the supported MQTT components, eg. binary_sensor.
  • <node_id> (Optional): ID of the node providing the topic, this is not used by Home Assistant but may be used to structure the MQTT topic. The ID of the node must only consist of characters from the character class [a-zA-Z0-9_-] (alphanumerics, underscore and hyphen).
  • <object_id>: The ID of the device. This is only to allow for separate topics for each device and is not used for the entity_id. The ID of the device must only consist of characters from the character class [a-zA-Z0-9_-] (alphanumerics, underscore and hyphen).

The <node_id> level can be used by clients to only subscribe to their own (command) topics by using one wildcard topic like <discovery_prefix>/+/<node_id>/+/set.

Best practice for entities with a unique_id is to set <object_id> to unique_id and omit the <node_id>.

Discovery payload

The payload must be a serialized JSON dictionary and will be checked like an entry in your configuration.yaml file if a new device is added, with the exception that unknown configuration keys are allowed but ignored. This means that missing variables will be filled with the platform’s default values. All configuration variables which are required must be present in the payload. The reason for allowing unknown documentation keys is allow some backwards compatibility, software generating MQTT discovery messages can then be used with older Home Assistant versions which will simply ignore new features.

Subsequent messages on a topic where a valid payload has been received will be handled as a configuration update, and a configuration update with an empty payload will cause a previously discovered device to be deleted.

A base topic ~ may be defined in the payload to conserve memory when the same topic base is used multiple times. In the value of configuration variables ending with _topic, ~ will be replaced with the base topic, if the ~ occurs at the beginning or end of the value.

Configuration variable names in the discovery payload may be abbreviated to conserve memory when sending a discovery message from memory constrained devices.

Supported abbreviations:

    'act_t':               'action_topic',
    'act_tpl':             'action_template',
    'atype':               'automation_type',
    'aux_cmd_t':           'aux_command_topic',
    'aux_stat_tpl':        'aux_state_template',
    'aux_stat_t':          'aux_state_topic',
    'av_tones':            'available_tones',
    'avty'                 'availability',
    'avty_mode':           'availability_mode',
    'avty_t':              'availability_topic',
    'avty_tpl':            'availability_template',
    'away_mode_cmd_t':     'away_mode_command_topic',
    'away_mode_stat_tpl':  'away_mode_state_template',
    'away_mode_stat_t':    'away_mode_state_topic',
    'b_tpl':               'blue_template',
    'bri_cmd_t':           'brightness_command_topic',
    'bri_cmd_tpl':         'brightness_command_template',
    'bri_scl':             'brightness_scale',
    'bri_stat_t':          'brightness_state_topic',
    'bri_tpl':             'brightness_template',
    'bri_val_tpl':         'brightness_value_template',
    'clr_temp_cmd_tpl':    'color_temp_command_template',
    'bat_lev_t':           'battery_level_topic',
    'bat_lev_tpl':         'battery_level_template',
    'chrg_t':              'charging_topic',
    'chrg_tpl':            'charging_template',
    'clr_temp_cmd_t':      'color_temp_command_topic',
    'clr_temp_stat_t':     'color_temp_state_topic',
    'clr_temp_tpl':        'color_temp_template',
    'clr_temp_val_tpl':    'color_temp_value_template',
    'cln_t':               'cleaning_topic',
    'cln_tpl':             'cleaning_template',
    'cmd_off_tpl':         'command_off_template',
    'cmd_on_tpl':          'command_on_template',
    'cmd_t':               'command_topic',
    'cmd_tpl':             'command_template',
    'cod_arm_req':         'code_arm_required',
    'cod_dis_req':         'code_disarm_required',
    'cod_trig_req':        'code_trigger_required',
    'curr_temp_t':         'current_temperature_topic',
    'curr_temp_tpl':       'current_temperature_template',
    'dev':                 'device',
    'dev_cla':             'device_class',
    'dock_t':              'docked_topic',
    'dock_tpl':            'docked_template',
    'e':                   'encoding',
    'ent_cat':             'entity_category,
    'err_t':               'error_topic',
    'err_tpl':             'error_template',
    'fanspd_t':            'fan_speed_topic',
    'fanspd_tpl':          'fan_speed_template',
    'fanspd_lst':          'fan_speed_list',
    'flsh_tlng':           'flash_time_long',
    'flsh_tsht':           'flash_time_short',
    'fx_cmd_t':            'effect_command_topic',
    'fx_cmd_tpl':          'effect_command_template',
    'fx_list':             'effect_list',
    'fx_stat_t':           'effect_state_topic',
    'fx_tpl':              'effect_template',
    'fx_val_tpl':          'effect_value_template',
    'exp_aft':             'expire_after',
    'fan_mode_cmd_tpl':    'fan_mode_command_template',
    'fan_mode_cmd_t':      'fan_mode_command_topic',
    'fan_mode_stat_tpl':   'fan_mode_state_template',
    'fan_mode_stat_t':     'fan_mode_state_topic',
    'frc_upd':             'force_update',
    'g_tpl':               'green_template',
    'hold_cmd_tpl':        'hold_command_template',
    'hold_cmd_t':          'hold_command_topic',
    'hold_stat_tpl':       'hold_state_template',
    'hold_stat_t':         'hold_state_topic',
    'hs_cmd_t':            'hs_command_topic',
    'hs_stat_t':           'hs_state_topic',
    'hs_val_tpl':          'hs_value_template',
    'ic':                  'icon',
    'init':                'initial',
    'hum_cmd_t':           'target_humidity_command_topic',
    'hum_cmd_tpl':         'target_humidity_command_template',
    'hum_stat_t':          'target_humidity_state_topic',
    'hum_stat_tpl':        'target_humidity_state_template',
    'json_attr':           'json_attributes',
    'json_attr_t':         'json_attributes_topic',
    'json_attr_tpl':       'json_attributes_template',
    'max_mirs':            'max_mireds',
    'min_mirs':            'min_mireds',
    'max_temp':            'max_temp',
    'min_temp':            'min_temp',
    'max_hum':             'max_humidity',
    'min_hum':             'min_humidity',
    'mode_cmd_tpl':        'mode_command_template',
    'mode_cmd_t':          'mode_command_topic',
    'mode_stat_tpl':       'mode_state_template',
    'mode_stat_t':         'mode_state_topic',
    'modes':               'modes',
    'name':                'name',
    'obj_id':              'object_id',
    'off_dly':             'off_delay',
    'on_cmd_type':         'on_command_type',
    'opt':                 'optimistic',
    'osc_cmd_t':           'oscillation_command_topic',
    'osc_cmd_tpl':         'oscillation_command_template',
    'osc_stat_t':          'oscillation_state_topic',
    'osc_val_tpl':         'oscillation_value_template',
    'pct_cmd_t':           'percentage_command_topic',
    'pct_cmd_tpl':         'percentage_command_template',
    'pct_stat_t':          'percentage_state_topic',
    'pct_val_tpl':         'percentage_value_template',
    'pl':                  'payload',
    'pl_arm_away':         'payload_arm_away',
    'pl_arm_home':         'payload_arm_home',
    'pl_arm_custom_b':     'payload_arm_custom_bypass',
    'pl_arm_nite':         'payload_arm_night',
    'pl_avail':            'payload_available',
    'pl_cln_sp':           'payload_clean_spot',
    'pl_cls':              'payload_close',
    'pl_disarm':           'payload_disarm',
    'pl_home':             'payload_home',
    'pl_lock':             'payload_lock',
    'pl_loc':              'payload_locate',
    'pl_not_avail':        'payload_not_available',
    'pl_not_home':         'payload_not_home',
    'pl_off':              'payload_off',
    'pl_on':               'payload_on',
    'pl_open':             'payload_open',
    'pl_osc_off':          'payload_oscillation_off',
    'pl_osc_on':           'payload_oscillation_on',
    'pl_paus':             'payload_pause',
    'pl_stop':             'payload_stop',
    'pl_strt':             'payload_start',
    'pl_stpa':             'payload_start_pause',
    'pl_ret':              'payload_return_to_base',
    'pl_rst_hum':          'payload_reset_humidity',
    'pl_rst_mode':         'payload_reset_mode',    
    'pl_rst_pct':          'payload_reset_percentage',
    'pl_rst_pr_mode':      'payload_reset_preset_mode',
    'pl_toff':             'payload_turn_off',
    'pl_ton':              'payload_turn_on',
    'pl_trig':             'payload_trigger',
    'pl_unlk':             'payload_unlock',
    'pos_clsd':            'position_closed',
    'pos_open':            'position_open',
    'pow_cmd_t':           'power_command_topic',
    'pow_stat_t':          'power_state_topic',
    'pow_stat_tpl':        'power_state_template',
    'pr_mode_cmd_t':       'preset_mode_command_topic',
    'pr_mode_cmd_tpl':     'preset_mode_command_template',
    'pr_mode_stat_t':      'preset_mode_state_topic',
    'pr_mode_val_tpl':     'preset_mode_value_template',
    'pr_modes':            'preset_modes',
    'r_tpl':               'red_template',
    'ret':                 'retain',
    'rgb_cmd_tpl':         'rgb_command_template',
    'rgb_cmd_t':           'rgb_command_topic',
    'rgb_stat_t':          'rgb_state_topic',
    'rgb_val_tpl':         'rgb_value_template',
    'send_cmd_t':          'send_command_topic',
    'send_if_off':         'send_if_off',
    'set_fan_spd_t':       'set_fan_speed_topic',
    'set_pos_tpl':         'set_position_template',
    'set_pos_t':           'set_position_topic',
    'pos_t':               'position_topic',
    'pos_tpl':             'position_template',
    'spd_rng_min':         'speed_range_min',
    'spd_rng_max':         'speed_range_max',
    'src_type':            'source_type',
    'stat_cla':            'state_class',
    'stat_clsd':           'state_closed',
    'stat_closing':        'state_closing',
    'stat_off':            'state_off',
    'stat_on':             'state_on',
    'stat_open':           'state_open',
    'stat_opening':        'state_opening',
    'stat_stopped':        'state_stopped',
    'stat_locked':         'state_locked',
    'stat_unlocked':       'state_unlocked',
    'stat_t':              'state_topic',
    'stat_tpl':            'state_template',
    'stat_val_tpl':        'state_value_template',
    'stype':               'subtype',
    'sup_duration':        'support_duration',
    'sup_vol':             'support_volume_set',
    'sup_feat':            'supported_features',
    'sup_off':             'supported_turn_off',
    'swing_mode_cmd_tpl':  'swing_mode_command_template',
    'swing_mode_cmd_t':    'swing_mode_command_topic',
    'swing_mode_stat_tpl': 'swing_mode_state_template',
    'swing_mode_stat_t':   'swing_mode_state_topic',
    'temp_cmd_tpl':        'temperature_command_template',
    'temp_cmd_t':          'temperature_command_topic',
    'temp_hi_cmd_tpl':     'temperature_high_command_template',
    'temp_hi_cmd_t':       'temperature_high_command_topic',
    'temp_hi_stat_tpl':    'temperature_high_state_template',
    'temp_hi_stat_t':      'temperature_high_state_topic',
    'temp_lo_cmd_tpl':     'temperature_low_command_template',
    'temp_lo_cmd_t':       'temperature_low_command_topic',
    'temp_lo_stat_tpl':    'temperature_low_state_template',
    'temp_lo_stat_t':      'temperature_low_state_topic',
    'temp_stat_tpl':       'temperature_state_template',
    'temp_stat_t':         'temperature_state_topic',
    'temp_unit':           'temperature_unit',
    'tilt_clsd_val':       'tilt_closed_value',
    'tilt_cmd_t':          'tilt_command_topic',
    'tilt_cmd_tpl':        'tilt_command_template',
    'tilt_inv_stat':       'tilt_invert_state',
    'tilt_max':            'tilt_max',
    'tilt_min':            'tilt_min',
    'tilt_opnd_val':       'tilt_opened_value',
    'tilt_opt':            'tilt_optimistic',
    'tilt_status_t':       'tilt_status_topic',
    'tilt_status_tpl':     'tilt_status_template',
    't':                   'topic',
    'uniq_id':             'unique_id',
    'unit_of_meas':        'unit_of_measurement',
    'val_tpl':             'value_template',
    'whit_val_cmd_t':      'white_value_command_topic',
    'whit_val_scl':        'white_value_scale',
    'whit_val_stat_t':     'white_value_state_topic',
    'whit_val_tpl':        'white_value_template',
    'xy_cmd_t':            'xy_command_topic',
    'xy_stat_t':           'xy_state_topic',
    'xy_val_tpl':          'xy_value_template',

Supported abbreviations for device registry configuration:

    'cu':                  'configuration_url'
    'cns':                 'connections',
    'ids':                 'identifiers',
    'name':                'name',
    'mf':                  'manufacturer',
    'mdl':                 'model',
    'hw':                  'hw_version',
    'sw':                  'sw_version',
    'sa':                  'suggested_area',

Support by third-party tools

The following software has built-in support for MQTT discovery:

Examples

Motion detection (binary sensor)

A motion detection device which can be represented by a binary sensor for your garden would send its configuration as JSON payload to the Configuration topic. After the first message to config, then the MQTT messages sent to the state topic will update the state in Home Assistant.

  • Configuration topic: homeassistant/binary_sensor/garden/config
  • State topic: homeassistant/binary_sensor/garden/state
  • Payload: {"name": "garden", "device_class": "motion", "state_topic": "homeassistant/binary_sensor/garden/state"}
  • Retain: The -r switch is added to retain the configuration topic in the broker. Without this, the sensor will not be available after Home Assistant restarts.

To create a new sensor manually.

mosquitto_pub -r -h 127.0.0.1 -p 1883 -t "homeassistant/binary_sensor/garden/config" -m '{"name": "garden", "device_class": "motion", "state_topic": "homeassistant/binary_sensor/garden/state"}'

Update the state.

mosquitto_pub -h 127.0.0.1 -p 1883 -t "homeassistant/binary_sensor/garden/state" -m ON

Delete the sensor by sending an empty message.

mosquitto_pub -h 127.0.0.1 -p 1883 -t "homeassistant/binary_sensor/garden/config" -m ''

For more details please refer to the MQTT testing section.

Sensors

Setting up a sensor with multiple measurement values requires multiple consecutive configuration topic submissions.

  • Configuration topic no1: homeassistant/sensor/sensorBedroomT/config
  • Configuration payload no1: {"device_class": "temperature", "name": "Temperature", "state_topic": "homeassistant/sensor/sensorBedroom/state", "unit_of_measurement": "°C", "value_template": "{{ value_json.temperature}}" }
  • Configuration topic no2: homeassistant/sensor/sensorBedroomH/config
  • Configuration payload no2: {"device_class": "humidity", "name": "Humidity", "state_topic": "homeassistant/sensor/sensorBedroom/state", "unit_of_measurement": "%", "value_template": "{{ value_json.humidity}}" }
  • Common state payload: { "temperature": 23.20, "humidity": 43.70 }

Entities with command topics

Setting up a light, switch etc. is similar but requires a command_topic as mentioned in the MQTT switch documentation.

  • Configuration topic: homeassistant/switch/irrigation/config
  • State topic: homeassistant/switch/irrigation/state
  • Command topic: homeassistant/switch/irrigation/set
  • Payload: {"name": "garden", "command_topic": "homeassistant/switch/irrigation/set", "state_topic": "homeassistant/switch/irrigation/state"}
  • Retain: The -r switch is added to retain the configuration topic in the broker. Without this, the sensor will not be available after Home Assistant restarts.
mosquitto_pub -r -h 127.0.0.1 -p 1883 -t "homeassistant/switch/irrigation/config" \
  -m '{"name": "garden", "command_topic": "homeassistant/switch/irrigation/set", "state_topic": "homeassistant/switch/irrigation/state"}'

Set the state.

mosquitto_pub -h 127.0.0.1 -p 1883 -t "homeassistant/switch/irrigation/set" -m ON

Using abbreviations and base topic

Setting up a switch using topic prefix and abbreviated configuration variable names to reduce payload length.

  • Configuration topic: homeassistant/switch/irrigation/config
  • Command topic: homeassistant/switch/irrigation/set
  • State topic: homeassistant/switch/irrigation/state
  • Configuration payload: {"~": "homeassistant/switch/irrigation", "name": "garden", "cmd_t": "~/set", "stat_t": "~/state"}

Another example using abbreviations topic name and base topic

Setting up a light that takes JSON payloads, with abbreviated configuration variable names:

  • Configuration topic: homeassistant/light/kitchen/config

  • Command topic: homeassistant/light/kitchen/set

  • State topic: homeassistant/light/kitchen/state

  • Example state payload: {"state": "ON", "brightness": 255}

  • Configuration payload:

    {
      "~": "homeassistant/light/kitchen",
      "name": "Kitchen",
      "unique_id": "kitchen_light",
      "cmd_t": "~/set",
      "stat_t": "~/state",
      "schema": "json",
      "brightness": true
    }
    

Use object_id to influence the entity id

The entity id is automatically generated from the entity’s name. All MQTT entity components optionally support providing an object_id which will be used instead if provided.

  • Configuration topic: homeassistant/sensor/device1/config
  • Example configuration payload:
{
  "name":"My Super Device",
  "object_id":"my_super_device",
  "state_topic": "homeassistant/sensor/device1/state"
 }

In the example above, the entity_id will be sensor.my_super_device instead of sensor.device1.