The REST Custom sensor queries a Representational State Transfer (REST) application programming interface (API) endpoint and maps the JavaScript Object Notation (JSON) or Extensible Markup Language (XML) result to sensor values.
The mapping rule must be available as a REST configuration file in JSON template (*.template) format according to the PRTG API definition for custom sensors.
REST Custom Sensor
For a detailed list and descriptions of the channels that this sensor can show, see section Channel List.
Sensor in Other Languages
Dutch: REST Aangepast
French: REST personnalisé
German: REST (Benutzerdef.)
Japanese: REST カスタム
Portuguese: REST (customizado)
Russian: Специальные настройки REST
Simplified Chinese: REST 自定义
Spanish: REST (personalizado)
Remarks
You must store the REST configuration file that contains the mapping rules on the probe system. In a cluster, copy the file to every cluster node.
This sensor does not officially support more than 50 channels. Depending on the data used with this sensor, you might exceed the maximum number of supported channels. In this case, PRTG tries to display all channels. Be aware, however, that you experience limited usability and performance. If you have more than 50 channel mappings in your REST configuration file, the sensor shows an error.
This sensor supports the IPv6 protocol.
This sensor has a medium performance impact.
In a cluster, status changes triggered by limits only work on the master node.
You cannot add this sensor to the hosted probe of a PRTG Hosted Monitor instance. If you want to use this sensor, add it to a remote probe device.
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.
REST Specific
Setting
Description
REST Configuration
Select a REST configuration file from the list. The sensor uses it to map the JSON or XML result from the REST query to sensor values.
The default REST configuration file is channelDiscovery. If you select this file, the sensor parses the returned JSON or XML and automatically creates channels based on available values: one channel for each number and boolean for strings if they are convertible into numbers.
This list shows all REST configuration files that are available in the \Custom Sensors\rest subfolder of the PRTG program directory on the probe system. For the files to appear in this list, store the files as JSON template (*.template) in this subfolder.
To use custom REST configurations in PRTG Hosted Monitor, contact the Paessler support team, or add this sensor to a remote probe instead and save the file on the remote probe system.
To show the expected values and sensor status, your files must return the expected JSON format. Channels, values, and messages must be embedded in valid JSON using JSONPath. For details, see section Define Channels and Select Channel Values.
For detailed information on how to create custom sensors and for the return format, see section Custom Sensors.
If you use custom sensors on the cluster probe, copy your files to every cluster node.
Basic Sensor Settings
Click the Settings tab of a sensor to change its settings.
If 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?
This setting is for your information only. You cannot change it.
Tags
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.
It is not possible to enter tags with a leading plus (+) or minus (-) sign, nor tags with parentheses (()) or angle brackets (<>).
For 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:
restcustomsensor
restsensor
Priority
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 () to the highest priority ().
Usually, 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.
REST Specific
REST Specific
Setting
Description
Request Method
Select an HTTP request method to determine how the sensor requests the REST API.
GET (default): Use the GET method to request the REST API.
POST: Use the POST method to request the REST API.
If you use the POST method, use the content type, for example application/x-www-form-urlencoded, as HTTP header. In section HTTP Headers, select Send custom HTTP headers and enter the content type in the Custom HTTP Headers field.
Postdata
This setting is only visible if you select POST above. Enter the data part for the POST request.
If you use the POST method, use the content type, for example application/x-www-form-urlencoded, as HTTP header. In section HTTP Headers, select Send custom HTTP headers and enter the content type in the Custom HTTP Headers field.
Request Protocol
Define the security protocol of the HTTP request:
HTTP (default): Send the REST query via HTTP (not secure).
HTTPS: Send the REST query via secure HTTPS.
Certificate Acceptance
This setting is only visible if you select HTTPS above. Select the kind of certificates that you want the sensor to accept for the connection:
Accept trusted certificates only (default): Accept only trusted certificates issued by a certificate authority (CA).
Accept all certificates: Accept all certificates, including self-signed certificates.
Authentication Method
Select the authentication method for access to the REST API:
No authentication (default): Do not use any authentication for the request.
Basic authentication: Use a user name and password for authentication.
Basic authentication with Windows credentials from parent device: Use the Windows credentials from the parent device. For more information, see section Inheritance of Settings.
Token: Use a JSON Web Token (JWT) or OAuth2 Bearer Token for authentication.
User Name
This setting is only visible if you select Basic authentication above. Enter a user name for the REST API. Enter a string.
Password
This setting is only visible if you select Basic authentication above. Enter a password for the REST API. Enter a string.
Token
This setting is only visible if you select Token above. Enter a JWT or OAuth2 Bearer Token that the REST API requires for authentication.
HTTP Headers
Define if you want to send custom HTTP headers to the target URL:
Do not send custom HTTP headers
Send custom HTTP headers
Custom HTTP Headers
This setting is only visible if you select Send custom HTTP headers above. Enter a list of custom HTTP headers with their respective values that you want to transmit to the target URL, each pair in one line. The syntax of a header-value pair is header1:value1.
If you enter more than one header-value pair, you must separate them with delimiters. The syntax is header1:value1|header2:value2|header3:value3
The sensor does not support the header field names user-agent, content-length, host.
Make sure that the HTTP header statement is valid. Otherwise, the sensor request cannot be successful.
If you select the POST as Request Method setting above, enter the content type, for example application/x-www-form-urlencoded, as the custom HTTP header.
Timeout (Sec.)
Enter a timeout in seconds for the request. Enter an integer. The maximum timeout value is 900 seconds (15 minutes).
If the reply takes longer than this value, the sensor cancels the request and shows a corresponding error message.
REST Query
Shows the REST query that this sensor executes. To change it, enter a valid query for the target REST API. The syntax is: [:port]/path[?var1=val1&...]
The sensor always inherits the first part of the address from the address of the parent device. Only enter the path to the REST endpoint of the parent device. You can override the port if necessary.
For example, if you add the sensor to a probe device, a query to the REST API of your PRTG installation that returns the number of sensors on the probe could look like this:
Shows the REST configuration file that the sensor uses to map the returned JSON or XML into sensor values.
PRTG shows this value for reference purposes only. If you need to change this value, add the sensor anew.
Debug Options
Debug Options
Setting
Description
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 names are Result of Sensor [ID].txt and Result of Sensor [ID].Data.txt. This setting is for debugging purposes. PRTG overwrites these files with each scanning interval.
This option is not available when the sensor runs on the hosted probe of a PRTG Hosted Monitor instance.
In a cluster, PRTG stores the result in the PRTG data directory of the master node.
Sensor Display
Sensor Display
Setting
Description
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.
You can set a different primary channel later by clicking 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. You 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.
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 under the corresponding setting name to disable the inheritance and to display its options.
The proxy settings determine how a sensor connects to a URL. You can enter data for an HTTP proxy server that sensors use when they connect via HTTP or HTTPS.
This setting only applies to HTTP sensors and how they monitor. To change the proxy settings for the PRTG core server, see section Core & Probes.
Proxy Settings for HTTP Sensors
For more information, see section Root Group Settings, section Proxy Settings for HTTP Sensors.
Scanning Interval
Scanning Interval
For more information, see section Root Group Settings, section Scanning Interval.
Schedules, Dependencies, and Maintenance Window
You 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
For more information, see section Root Group Settings, section Schedules, Dependencies, and Maintenance Window.
Access Rights
Access Rights
For more information, see section Root Group Settings, section Access Rights.
Channel Unit Configuration
Which 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
For more information, see section Root Group Settings, section Channel Unit Configuration.
Define Channels and Select Channel Values
In your REST configuration file, you must define which values of the returned JSON or XML are mapped to which channels.
A channel is defined by the channel key in your REST configuration. See the JSON Return Format: Minimum Example in section Custom Sensors.
A channel value is defined by an expression that retrieves and processes the value from the JSON source. The expression can contain JSONPath, gval operators, and functions.
Example
For this example, we take PRTG as REST endpoint and query the sensor status statistics for the local probe. The REST query that we enter in the sensor settings looks like this:
Your REST configuration has to translate this JSON for the sensor. It has to be available as JSON template (*template) in the \Custom Sensors\rest subfolder of the PRTG program directory on the probe system. See section Custom Sensors for details about the JSON return format.
The following example returns two channels from the JSON resource that are added to the sensor in PRTG, Total (total sensor count) and Alarms (sensors in the Down status), each selected by their keys in the returned JSON.
The channel values are the values of the corresponding properties of the REST result defined in JSONPath notation, $.sensorxref[0].totalsens (28) and $.sensorxref[0].downsens (0).
Each value's property (destination) and the text property is set to the appropriate transformation rules from source to destination. This is the JSON path of the source. The sensor replaces each path with the value from the source.
Several REST configuration files are available in the \Custom Sensors\rest subfolder by default. They are ready for use. You can also analyze them to see how to write your own REST configuration.
JSONPath
The REST Custom sensor uses JSONPath to assign values from the returned JSON to channels. With JSONPath, you provide the path to the value in the JSON source that you want to monitor in a channel.
The JSONPath implementation that PRTG uses for the REST Custom sensor might differ from other JSONPath implementations. You can test and debug your definitions using the command line. To test simple JSONPath expressions and calculations, you can also use JSONPath Online Evaluator, for example. Note that this tool might not work properly with complex JSONPath expressions that PRTG supports.
Example
To demonstrate the practical usage of JSONPath, we use this JSON example that a REST query might have returned as reference in this section.
You can modify matches with (<expression>) and keys with [<expression>].
Example
This expression matches true and false in the example above because only the first device has a beta channel:
$.devices[*](@.firmware.channel=="beta")
Placeholder
Placeholders give access to values of wildcards in a match. A placeholder #n (where n is a natural number) represents the value of the nth wildcard. You can use this in the keys of JSON arrays.
Example
This expression creates a JSON map from ids to the corresponding firmware channel and matches {"0.7":"beta"} in the example above:
{$.devices[#0].id:$.devices[*].channel}
This is an extension of the official JSONPath.
Constant
Numeric constants as 64-bit floating point: 12345.678
String constants with double quotes: "switch"
Boolean constants: true and false
Operator
Parentheses control the order of evaluation: (<expression>)
Arrays with brackets: [<expression>, <expression>, ...]
You can perform calculations with the values of the source JSON or XML. The sensor uses the Paessler gval package for the calculations. For details, refer to the gval documentation.
The following operators and functions are available to calculate channel values.
REST Custom Sensor: Operators
Operator
Description
Operand Type
Output Type
Infix Modifiers
+
plus
number
number
-
minus
number
number
*
times
number
number
**
power of
number
number
%
modulo
number
number
/
divide
number
number
&
bitwise and
number
number
|
bitwise or
number
number
^
bitwise xor
number
number
<<
shift left
number
number
>>
shift right
number
number
Logical Infix Operators
>
greater than
number/string
bool
>=
equal or greater than
number/string
bool
<
less than
number/string
bool
<=
equal or less than
number/string
bool
==
equal
any
bool
!=
not equal
any
bool
=~
match regular expression
string
bool
!~
mismatch regular expression
string
bool
in
contains element
any, array
bool
&&
and
and
bool
||
or
or
bool
??
coalescence
any
any
Prefix Operators
-
negative
number
number
~
bitwise not
number
number
!
not
bool
bool
REST Custom Sensor: Functions
duration(start,end)
Calculates the nanoseconds between start and end.
Both parameters must be RFC3339 date time strings.
This expression returns 1 because $.device[0].firmware.channel resolves to beta.
implode(array-/object-of-string, string)
Returns the concatenation of each string in the array, separated by the specified string.
Example
implode($..tx_bytes, ",")
This expression returns 7229493,7229472.
Generic Channels
You can create a template in your REST configuration that defines generic channels. Generic channels are created based on the data that the REST endpoint returns. When the returned value is an array or object, the sensor creates a channel for each element and concatenates the corresponding key to the channel name.
Example
Imagine that you want to have a total byte channel for each network card that is defined in the JSON example above. You can do this by creating a dynamic channel like in the following example.
Every channel must have a unique name. You cannot remove channels once they have been added and they keep their last received value. You can add new channels.
XML Sources
If the REST source returns XML instead of JSON, the sensor transforms the XML result to JSON before replacing the value paths with source values. Because of this, you do not know the structure of the source JSON to correctly provide the paths.
In this case, manually execute the sensor executable rest.exe from the \Sensor System subfolder of the PRTG program directory on the probe system. Execute rest.exe with the address of the XML endpoint and the parameter passthrough. The rest executable returns the converted XML to a JSON result that you can use to define the desired paths.
rest.exe <xml-endpoint-url> passthrough
Usage and Debugging
To create a suitable REST configuration for the sensor, you might want to check the returned JSON or XML and see what happens when your mapping rules apply.
The REST Custom sensor is an EXE sensor, so you can test and debug your configuration by executing rest.exe with several parameters. The rest.exe file is located in the \Sensor System subfolder of the PRTG program directory.
1 accepts self-signed certificates on HTTPS connections
-template
Returns the discovered template if you use channelDiscovery.
Channel List
Which channels the sensor actually shows might depend on the target device, the available components, and the sensor setup.
Channel
Description
Downtime
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
Response Time
The response time
This channel is the primary channel by default.
[Value]
The values that a REST API returns in several channels
For details about the return value format, see section Custom Sensors.