<%NUMBERING1%>.<%NUMBERING2%>.<%NUMBERING3%> PRTG Manual: MQTT Subscribe Custom Sensor

The MQTT Subscribe Custom sensor subscribes to a Message Queue Telemetry Transport (MQTT) topic and monitors up to ten numeric values from the received JavaScript Object Notation (JSON) data.

MQTT Subscribe Custom Sensor

MQTT Subscribe Custom Sensor

i_square_cyanFor a detailed list and descriptions of the channels that this sensor can show, see section Channel List.

Sensor in Other Languages

  • Dutch: MQTT Abonneren Aangepast
  • French: MQTT abonnement personnalisé
  • German: MQTT Subscribe (Benutzerdefiniert)
  • Japanese: MQTT サブスクライブカスタム
  • Portuguese: Assinatura customizada MQTT
  • Russian: Пользовательская подписка MQTT
  • Simplified Chinese: MQTT 订阅自定义
  • Spanish: Suscriptor MQTT personalizado


Consider the following remarks and requirements for this sensor:




  • This sensor requires credentials for MQTT.


  • This sensor supports IPv6.

Performance impact

  • This sensor has a medium performance impact.

Multi-platform probe

  • You can add this sensor to a multi-platform probe.

Add Sensor



Channel #1 Name

Enter a name for the channel.

i_round_blueYou can change this value later in the channel settings of this sensor.

Channel #1 Unit

Enter the unit for the numeric value that this sensor monitors.

i_round_blueYou can change this value later in the channel settings of this sensor.

Basic Sensor Settings

Basic Sensor Settings

Basic Sensor Settings

The sensor has the following default tags that are automatically predefined in the sensor's settings when you add the sensor:

  • mqtt
  • mqttsubscribecustom

i_square_cyanFor more information about basic sensor settings, see section Sensor Settings.

MQTT Specific

MQTT Specific

MQTT Specific




Enter the topic that you want to monitor.

i_round_blueThe sensor supports single-level (+) and multi-level (#) wildcards.

Time Since Last Message

Select if you want to add a channel that shows the time since the last message was received:

  • Disable (default): Do not create this channel.
  • Enable: Create this channel. The sensor remains in the Up status even if it received no messages during the last scan interval.

i_round_blueYou can define a threshold notification trigger to receive notifications if no data is received for a certain amount of time.

Last Message Handling

Define what PRTG does with the last message received if there are no new messages in the following scanning interval:

  • Dismiss (default): The sensor dismisses the last message received after a new scan.
  • Retain: The sensor saves the last message received until a new message is received.

Sensor Message JSONPath

Optionally enter the path to the value in the JSON data. The sensor shows the received value as the sensor message.

i_round_redThe data must be in valid JSON format. For details about the format, see Channel #x JSONPath below.

i_round_blueThe sensor only shows the received value if the sensor is in the Up status. If the sensor changes to the Down status, the sensor message shows the error message instead.

Channel #x JSONPath

Enter the path to the numeric value in the received JSON structure that you want to monitor.

i_round_redThe data must be in valid JSON format, for example like this:


"Sensor1": {"Temp":25,"Unit":"°C"},
"Sensor2": {"Humidity":36,"Unit":"%"}

To query temperature, enter the following JSONPath:


To query humidity, enter the following JSONPath:


Channel #x Value Type

Select the value type that the channel displays:

  • Absolute (integer): Integer64 values with or without an operational sign, such as 10 or 120 or -12 or 120.
  • Absolute (float): Double values, such as -5.80 or 8.23.
    i_round_blueIf you select Absolute (float), the sensor automatically shows all decimal places of the received value in the channel. You can define how many decimal places of the channel's data that you want to display in graphs and tables in the channel settings.
  • Delta (counter): Counter values. The sensor calculates the difference between the last and the current value. Enter an integer. The sensor additionally divides the delta value by a time period to indicate a speed value.
    i_round_redThis mode only works if the difference between the last and the current value is positive and increases with each scanning interval. This mode does not support negative values and decreasing values.

i_round_blueAbsolute (integer) and Absolute (float) support the extraction of numerical values from a received string. The sensor parses the numerical value from the beginning of the string until it encounters the first element that is not part of a numerical value, for example a letter. The sensor ignores whitespace characters.

i_round_blueYou cannot change this value after sensor creation.

Channel #2 - #10

You can define up to 10 channels. You must define at least one channel, so you see all available settings for Channel #1. Specify how to handle all other possible channels:

  • Disable (default): Do not create this channel.
  • Enable: Create this channel.

i_round_blueIf you select Disable (default), you can still see the channels, but they do not receive data anymore.

Sensor Display

Sensor Display

Sensor Display



Primary Channel

Select a channel from the list to define it as the primary channel. In the device tree, PRTG displays the last value of the primary channel below the sensor's name. The available options depend on what channels are available for this sensor.

i_round_blueYou can set a different primary channel later by clicking b_channel_primary below a channel gauge on the sensor's Overview tab.

Graph Type

Define how this sensor shows different channels:

  • Show channels independently (default): Show a graph for each channel.
  • Stack channels on top of each other: Stack channels on top of each other to create a multi-channel graph. This generates a graph that visualizes the different components of your total traffic.
    i_round_redYou cannot use this option in combination with manual Vertical Axis Scaling (available in the channel settings).

Stack Unit

This setting is only visible if you select Stack channels on top of each other above.

Select a unit from the list. PRTG stacks all channels with this unit on top of each other. By default, you cannot exclude single channels from stacking if they use the selected unit. However, there is an advanced procedure to do so.

Debug Options

Debug Options

Debug Options



Result Handling

Define what PRTG does with the sensor result:

  • Discard result (default): Do not store the sensor result.
  • Store result: Store the last sensor result in the \Logs\sensors subfolder of the PRTG data directory on the probe system. The file name is Result of Sensor [ID].log. This setting is for debugging purposes. PRTG overwrites this file with each scanning interval.

i_podThis option is not available when the sensor runs on the hosted probe of a PRTG Hosted Monitor instance.

i_round_blueIn a cluster, PRTG stores the result in the PRTG data directory of the master node.

Inherited Settings

By default, all of these settings are inherited from objects that are higher in the hierarchy. We recommend that you change them centrally in the root group settings if necessary. To change a setting for this object only, click b_inherited_enabled under the corresponding setting name to disable the inheritance and to display its options.

i_square_cyanFor more information, see section Inheritance of Settings.

Channel List

i_round_blueWhich channels the sensor actually shows might depend on the target device, the available components, and the sensor setup.




In the channel table on the Overview tab, this channel never shows any values. PRTG uses this channel in graphs and reports to show the amount of time in which the sensor was in the Down status


The returned numeric values in up to ten channels


i_square_blueKNOWLEDGE BASE

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