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

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This sensor requires credentials for MQTT in settings that are higher in the object hierarchy, for example, in the settings of the parent device.

This sensor supports the IPv6 protocol.

This sensor has a medium performance impact.

Add Sensor

The Add Sensor dialog appears when you manually add a new sensor to a device. It only shows the settings that are required to create the sensor. You can change nearly all settings on the sensor's Settings tab after creation.

MQTT Specific



Channel #1 Name

Enter a name for the channel.

i_round_blueAfter sensor creation, you can change the name of the channel in the channel settings under Name.

Channel #1 Unit

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

i_round_blueAfter sensor creation, you can change the unit in the channel settings under Unit.

Channel #1 - #10 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.

Delta (counter): Counter values. PRTG calculates the difference between the last and the current value. Enter an integer. PRTG 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_redIt is not possible to change the value type after sensor creation.

Channel #2 - #10

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

Disable: Do not create this channel.

Enable: Create this channel.

i_round_blueYou can add additional channels after creation in the sensor's Settings tab.

Basic Sensor Settings

Click the Settings tab of a sensor to change its settings.

Basic Sensor Settings

Basic Sensor Settings



Sensor Name

Enter a name to identify the sensor. By default, PRTG shows this name in the device tree, as well as in alarms, logs, notifications, reports, maps, libraries, and tickets.

i_round_blueIf the name contains angle brackets (<>), PRTG replaces them with braces ({}) for security reasons. For more information, see the Knowledge Base: What security features does PRTG include?

Parent Tags

Shows tags that the sensor inherits from its parent device, parent group, and parent probe.

i_round_blueThis setting is for your information only. You cannot change it.


Enter one or more tags. Confirm each tag with the Spacebar key, a comma, or the Enter key. You can use tags to group objects and use tag-filtered views later on. Tags are not case-sensitive. Tags are automatically inherited.

i_round_blueIt is not possible to enter tags with a leading plus (+) or minus (-) sign, nor tags with parentheses (()) or angle brackets (<>).

i_round_blueFor performance reasons, it can take some minutes until you can filter for new tags that you added.

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




Select a priority for the sensor. This setting determines the position of the sensor in lists. The highest priority is at the top of a list. Choose from the lowest priority (i_priority_1) to the highest priority (i_priority_5).

i_round_blueUsually, a sensor connects to the IP Address/DNS Name of the parent device. See the device settings for details. For some sensors, you can explicitly define the monitoring target in the 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.

Sensor Message JSONPath

Optionally enter the path to the value in the JSON data that the sensor shows as 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 string 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

Shows the value type that the channel displays.

i_round_bluePRTG shows this value for reference purposes only. If you need to change this value, add the sensor anew.

Channel #2 - #10

Shows if the channel is enabled or disabled. You can select Disable (default) if you no longer need the according channels. 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, the last value of the primary channel is always displayed 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 different channels are shown for this sensor:

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 enable Stack channels on top of each other as Graph Type. Select a unit from the list. All channels with this unit are stacked 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: 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.

Scanning Interval

Scanning Interval

Scanning Interval

i_square_cyanFor more information, see section Root Group Settings, section Scanning Interval.

Schedules, Dependencies, and Maintenance Window

i_round_blueYou cannot interrupt the inheritance for schedules, dependencies, and maintenance windows. The corresponding settings from the parent objects are always active. However, you can define additional schedules, dependencies, and maintenance windows. They are active at the same time as the parent objects' settings.

Schedules, Dependencies, and Maintenance Window

Schedules, Dependencies, and Maintenance Window

i_square_cyanFor more information, see section Root Group Settings, section Schedules, Dependencies, and Maintenance Window.

Access Rights

Access Rights

Access Rights

i_square_cyanFor more information, see section Root Group Settings, section Access Rights.

Channel Unit Configuration

i_round_blueWhich channel units are available depends on the sensor type and the available parameters. If no configurable channels are available, this field shows No configurable channels.

Channel Unit Configuration

Channel Unit Configuration

i_square_cyanFor more information, see section Root Group Settings, section Channel Unit Configuration.

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

What security features does PRTG include?