<%NUMBERING1%>.<%NUMBERING2%>.<%NUMBERING3%> PRTG Manual: REST Custom v2 Sensor

The REST Custom v2 sensor queries a JavaScript Object Notation (JSON) or Extensible Markup Language (XML) Representational State Transfer (REST) application programming interface (API) endpoint and maps the JSON or XML result to sensor values.

i_betaThis sensor is in beta status. The operating methods and the available settings are still subject to change. Do not expect that all functions work properly, or that this sensor works as expected at all.

REST Custom v2 Sensor

REST Custom v2 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: REST Aangepast v2
  • French: REST personnalisé v2
  • German: REST (Benutzerdefiniert) v2
  • Japanese: REST カスタム v2
  • Portuguese: REST (customizado) v2
  • Russian: Специальные настройки REST v2
  • Simplified Chinese: REST 自定义 v2
  • Spanish: REST (personalizado) v2

Remarks

Consider the following remarks and requirements for this sensor:

Remark

Description

Enabled Beta Sensors experimental feature

This sensor requires that the Beta Sensors experimental feature is enabled.

i_square_cyanFor more information, see the Knowledge Base: What are beta sensors and how can I use them?

JSONPath and XPath version

This sensor supports JSONPath and XPath 1.0.

Smart URL replacement

This sensor supports smart URL replacement.

IPv6

This sensor supports IPv6.

Performance impact

This sensor has a very low performance impact.

Lookups

This sensor uses lookups to determine the status values of one or more channels.

Credentials

You can define credentials for REST API in settings that are higher in the object hierarchy.

Multi-platform probe

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

Limitations

  • Strings that contain angled brackets (< and >) cannot be mapped manually. This affects the following settings: Channel #x Strings mapped to the 'Up' status, Channel #x Strings mapped to the 'Warning' status, and Channel #x Strings mapped to the 'Down' status. We are already working on a solution.

Add Sensor

Setting

Description

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:

i_round_blueIt is not possible to enable or disable channels after sensor creation.

Channel #x JSONPath/XPath

Enter the JSONPath or XPath of the JSON or XML result that you want to monitor.

JSONPath example:

$.store.book[0].year

XPath example:

/store/book[1]/year

Channel #x Name

Enter a name for the channel. Enter a string. For example, Total.

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?

Channel #x Unit

Enter the unit for the value that this sensor monitors. For example, #.

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:

  • rest

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

REST Specific

REST Specific

REST Specific

Setting

Description

Request URL

Enter the URL of the JSON or XML REST API endpoint that you want to request.

Example URL:

https://:1616/api/health?token=%restbearertoken&name=%restusername&refresh=true

i_round_blueYou can use the following placeholders in this field: %restusername, %restpassword, %restbearertoken, %restplaceholder1, %restplaceholder2, %restplaceholder3, %restplaceholder4, and %restplaceholder5. You can define these placeholders in the credentials for REST API in settings that are higher in the object hierarchy.

i_square_cyanPRTG uses a smart URL replacement with which you can use the parent device's IP address or Domain Name System (DNS) name setting as part of the URL. For more information, see section Smart URL Replacement.

i_round_blueIf you enter 127.0.0.1 as IP address of the parent device, PRTG requests the following URL:

https://127.0.0.1:1616/api/health?token=%restbearertoken&name=%restusername&refresh=true

Request Method

Select the HTTP request method that the sensor uses to request the REST API:

  • GET (default): Use the GET method to request the REST API.
  • POST: Use the POST method to request the REST API.

POST Body

This setting is only visible if you select POST above.

Enter the data part for the POST request.

i_round_blueYou can use the following placeholders in this field: %restusername, %restpassword, %restbearertoken, %restplaceholder1, %restplaceholder2, %restplaceholder3, %restplaceholder4, and %restplaceholder5. You can define these placeholders in the credentials for REST API in settings that are higher in the object hierarchy.

Custom Headers

Enter a list of custom HTTP headers with their respective values that you want to transmit to the target URL. The syntax of a header-value pair is header1:value1.

Custom header example:

host:host1.example.com
User-Agent:PRTG sensor 0.1
X-API-Key: %restplaceholder1

i_round_redIf you enter more than one header-value pair, enter each pair in one line:
header1:value1
header2:value2
header3:value3

i_round_redMake sure that the HTTP header statement is valid. Otherwise, the sensor request cannot be successful.

i_round_blueYou can use the following placeholders in this field: %restusername, %restpassword, %restbearertoken, %restplaceholder1, %restplaceholder2, %restplaceholder3, %restplaceholder4, and %restplaceholder5. You can define these placeholders in the credentials for REST API in settings that are higher in the object hierarchy.

Timeout (Sec.)

Enter a timeout in seconds for the request. Enter an integer. The maximum timeout value is 900 seconds (15 minutes).

i_round_blueIf the reply takes longer than this value, the sensor cancels the request and shows a corresponding error message.

Content Type

Select the type of the content that the sensor queries:

  • JSON (default)
  • XML

Custom Sensor Message

Enter the JSONPath or XPath from which you want to receive a string that the sensor shows as the permanent sensor message.

JSONPath example:

$.store.book[0].title

XPath example:

/store/book[1]/title

Channel Settings

Channel Settings

Channel Settings

Setting

Description

Channel #x JSONPath/XPath

Enter the JSONPath or XPath of the JSON or XML result that you want to monitor.

JSONPath example:

$.store.book[0].year

XPath example:

/store/book[1]/year

Channel #x Name

Enter a name for the channel. Enter a string. For example, Total. PRTG dynamically generates channels with this name as the identifier.

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?

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.
  • Status (string): The sensor shows a status depending on how you map the returned strings and shows the returned strings as sensor message.
  • Lookup: The sensors shows a status depending on how you define values in a custom lookup file.

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 #x Unit

This setting is only visible if you select Absolute (integer), Absolute (float), or Delta (counter) as Channel #x Value Type.

Select the unit that the channel displays:

  • Custom (default)
  • Percent
  • Percent (CPU)
  • Temperature (celsius)
  • Time (milliseconds)
  • Time (hours)
  • Time (seconds)
  • Bytes (memory)
  • Bytes (disk)
  • Bytes (file)
  • Bytes (bandwidth)
  • Bytes per second (disk)
  • Bytes per second (network)

i_round_blueYou cannot change this value after sensor creation.

Channel #x Custom Unit

This setting is only visible if you select Custom (default) as Channel #x Unit.

Enter the custom unit of the value of this channel. Enter a string.

Channel #x Strings mapped to the 'Up' status

This setting is only visible if you select Status (string) as Channel #x Value Type.

Enter the strings that the sensor maps to the Up status in a comma-separated list.

i_round_blueIf a string contains a comma, you must put the string in quotation marks. For example, to map the string Friday,2nd enter "Friday,2nd". If a string contains quotation marks, you must escape the quotation marks using a backslash (\) and put the string in quotation marks. For example, to map the string Friday "2nd" enter "Friday \"2nd\"".

Channel #x Strings mapped to the 'Warning' status

This setting is only visible if you select Status (string) as Channel #x Value Type.

Enter the strings that the sensor maps to the Warning status in a comma-separated list.

i_round_blueIf a string contains a comma, you must put the string in quotation marks. For example, to map the string Friday,2nd enter "Friday,2nd". If a string contains quotation marks, you must escape the quotation marks using a backslash (\) and put the string in quotation marks. For example, to map the string Friday "2nd" enter "Friday \"2nd\"".

Channel #x Strings mapped to the 'Down' status

This setting is only visible if you select Status (string) as Channel #x Value Type.

Enter the strings that the sensor maps to the Down status in a comma-separated list.

i_round_blueIf a string contains a comma, you must put the string in quotation marks. For example, to map the string Friday,2nd enter "Friday,2nd". If a string contains quotation marks, you must escape the quotation marks using a backslash (\) and put the string in quotation marks. For example, to map the string Friday "2nd" enter "Friday \"2nd\"".

Channel #x Handling of Unknown Strings

This setting is only visible if you select Status (string) as Channel #x Value Type.

Select the status to which the sensor maps all unknown strings in the returned result that are not manually mapped to the Up, the Warning, or the Down status:

  • 'Up' status: Map all unknown strings to the Up status.
  • 'Warning' status: Map all unknown strings to the Warning status.
  • 'Down' status (default): Map all unknown strings to the Down status.

Channel #x Lookup ID

This setting is only visible if you select Lookup as Channel #x Value Type.

Enter the ID of the lookup you wish to use. You can find the ID in the ValueLookup parameter in the lookup file.

i_square_cyanFor more information, see section Define Lookups.

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: Do not create this channel.
  • Enable: Create this channel.

i_round_blueIt is not possible to enable or disable channels after sensor creation.

Sensor Display

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, 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

Setting

Description

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.

JSONPath

The REST Custom v2 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.

i_round_blueThe JSONPath implementation that PRTG uses for the REST Custom v2 sensor might differ from other JSONPath implementations. To test simple JSONPath expressions and calculations, you can use JSONPath Online Evaluator - jsonpath.com, for example. Note that this tool might not work properly with complex JSONPath expressions that PRTG supports.

i_speechExample

To demonstrate the practical usage of JSONPath, we use this JSON example that a REST query might have returned as reference in this section.

{
"devices":[
 {
   "firmware":{
     "id":"0.7",
     "date":"2017-05-18T17:11:43.7049944Z",
     "channel": "beta"
   },
   "networks": {
     "a": {
       "rx_bytes": 35985021,
       "rx_packets": 176791,
       "rx_errors": 0,
       "rx_dropped": 476,
       "tx_bytes": 7229493,
       "tx_packets": 35518,
       "tx_errors": 0,
       "tx_dropped": 1
     },
     "b": {
       "rx_bytes": 40085321,
       "tx_bytes": 55294975
     }
   }
 },
 {
   "networks": {
     "a": {
       "rx_bytes": 63685865,
       "tx_bytes": 7229472
     }
   }
 }
 ]
}

REST Custom v2 Sensor: JSONPath

Root

The dollar sign ($) matches the root element of the JSON data.

Child

You can match a child with .<key> or [<key>].

  • .<key> must only contain letters, numbers, and underscore (_). Hyphens (-) must be escaped with quotation marks.
  • [<key>] must only contain a number or a quoted string.

i_speechExample

This expression matches 35985021 in the example above:

$.devices.0.networks.a.rx_bytes

You get the same result with this expression:

$["devices"][0]["networks"]["a"]["rx_bytes"]

If an element contains a hyphen (-), the .<key> notation does not work. Use the [<key>] notation in this case:

$["data"][0]["system-stats"]["temps"]["Board (CPU)"]

Wildcard

To match multiple values, you can use the asterisk symbol (*).

  • .*
  • [*]

i_speechExample

This expression matches 35985021 and 40085321 in the example above:

$.devices[0].networks.*.rx_bytes

Recursive Descent

You can match all subitems of a node with two dots (..).

i_speechExample

This expression matches 7229493 and 55294975 and 7229472 in the example above:

$..tx_bytes

Union

You can match multiple children with [<key1>,<key2>,<...>].

i_speechExample

This expression matches 35985021 and 7229493 in the example above:

$.devices.0.networks.a["rx_bytes","tx_bytes"]

Slice

You can match multiple children of an array with [<begin>:<end>] or [<begin>:<end>:<step>].

  • By default, begin, end, and step are either integers or empty.
  • The default approach is to go step by step from the first array element to the last element.
  • Step can also be a negative integer to go through the array in reversed order.

i_speechExample

This expression matches 63685865 and 7229472 in the example above:

$.devices[-1:].networks.a[rx_bytes,tx_bytes]

Current

The @ symbol matches the current element.

i_speechExample

This expression matches 63685865 and 7229472 in the example above:

$.devices[(@.length-1)].networks.a.rx_bytes

Filter

You can filter matches with [?<expression>].

i_speechExample

This expression matches 35985021 in the example above because the first device is the only one with a beta channel:

$.devices[?(@.firmware.channel=="beta")].networks.a.rx_bytes

Constant

  • Numeric constants as 64-bit floating point: 12345.678
  • String constants with double quotation marks ("): "switch"
  • Boolean constants: true and false
    i_round_blueIf the JSONPath points to a boolean, the sensor translates true as 1 and false as 0.

Functions

You can use functions on top level or in filters.

This expression returns the number items in the element devices in the example above:

length($.devices)

i_round_blueFor more information about functions, see JsonCons JSONPath | Functions.

Operator

  • Parentheses control the order of evaluation: (<expression>)
  • Arrays with brackets: [<expression>, <expression>, ...]
  • Objects: {<expression>:<expression>, <expression>:<expression>, ...}

i_round_blueFor more information about JSONPath, see JsonCons JSONPath.

REST Custom v2 Sensor: XPath

i_speechExample

To demonstrate the practical usage of XPath, we use this XML example that a REST query might have returned as reference in this section.

<?xml version="1.0" encoding="UTF-8" ?>
<root>
 <devices>
   <firmware>
     <id type="major">0</id>
     <id type="minor">7</id>
     <date>2017-05-18T17:11:43.7049944Z</date>
     <channel>beta</channel>
   </firmware>
   <networks>
     <a>
       <rx_bytes>35985021</rx_bytes>
       <rx_packets>176791</rx_packets>
       <rx_errors>0</rx_errors>
       <rx_dropped>476</rx_dropped>
       <tx_bytes>7229493</tx_bytes>
       <tx_packets>35518</tx_packets>
       <tx_errors>0</tx_errors>
       <tx_dropped>1</tx_dropped>
     </a>
     <b>
       <rx_bytes>40085321</rx_bytes>
       <tx_bytes>55294975</tx_bytes>
     </b>
   </networks>
 </devices>
 <devices>
   <networks>
     <a>
       <rx_bytes>63685865</rx_bytes>
       <tx_bytes>7229472</tx_bytes>
     </a>
   </networks>
 </devices>
</root>

REST Custom v2 Sensor: XPath

Root

The slash symbol (/) matches the root element of the XML data.

Child

You can match a child by its name with /<key> or [<key>] or by its index with [<index>].

  • /<key> must only contain letters, numbers, and underscore (_). Hyphens (-) must be escaped with quotation marks.
  • [<key>] must only contain a number or a quoted string.
  • [<index>] must only contain a number.

i_speechExample

This expression matches 35985021 in the example above:

/root/devices[1]/networks/a/rx_bytes

This expression matches major in the example above:

/root/devices[1]/firmware/id[1]/@type

Wildcard

To match multiple values, you can use the asterisk symbol (*).

  • /*
  • /@*
  • [*]
  • [@*]

i_speechExample

This expression matches 35985021 and 40085321 in the example above:

/root/devices[1]/networks/*/rx_bytes

Recursive Descent

You can match all subitems of a node with two slashes (//).

i_speechExample

This expression matches 7229493 and 55294975 and 7229472 in the example above:

//tx_bytes

Union

You can match multiple queries by combining them with the vertical bar symbol (|).

i_speechExample

This expression matches 35985021 and 7229493 in the example above:

/root/devices[1]/networks/a/rx_bytes | /root/devices[1]/networks/a/tx_bytes

Filter

You can filter matches with [<expression>].

i_speechExample

This expression matches 35985021 in the example above because the first device is the only one with a beta channel:

/root/devices[firmware/channel='beta']/networks/a/rx_bytes

This expression matches 0 in the example above:

/root/devices[1]/firmware[1]/id[@type='major']

Constant

  • Numeric constants as 64-bit floating point: 12345.678
  • String constants with double quotation marks ("): "switch"
  • Boolean constants: true and false
    i_round_blueIf the XPath points to a boolean, the sensor translates true as 1 and false as 0.

Functions

You can use functions on top level or in filters.

This expression returns the number of items in the devices element in the example above:

count(/root/devices[position() < 3])

i_round_blueFor more information about functions, see XML Path Language (Core Function Library).

Operator

  • Parentheses control the order of evaluation: (<expression>)

i_round_blueFor more information about XPath, see XML Path Language (XPath).

Calculating Channel Values

The REST Custom v2 sensor supports the following arithmetic:

  • Addition (+)
  • Subtraction (-)
  • Multiplication (*)
  • Division (div, /)
  • Equal (=)
  • Not equal (!=)

i_speechExamples

XML

JSON

<root>
<one>1</one>
<two value_int="2">2</two>
<two_point5>2.5</two_point5>
<four>4</four>
</root>

{
 "root": {
   "one": 1,
   "two": 2,
   "two_string": "2",
   "two_point5": 2.5,
   "four": 4
 }
}

XML

JSON

Description

Result (XML)

Result (JSON)

/root/one + /root/two

eval($.root.one + $.root.two)

Addition of the numbers

3

3

n/a

eval($.root.one + to_number($.root.two_string))

Addition of a number and a string

n/a

3

/root/one + /root/two/@value_int

n/a

Addition of a number and an attribute value

3

n/a

/root/four div /root/two

eval($.root.four / $.root.two)

Division of two integers. The expected result is an integer

2

2

/root/one div /root/two

eval($.root.one / $.root.two)

Division of two integers, the expected result is a floating-point number

0.5

0

n/a

eval($.root.one / $.root.two * 1.0)

Division of two integers with a floating point number as result

n/a

0.5

/root/one div /root/two_point5

eval($.root.one / $root.two_point5)

Division of a float and an integer

0.4

0.4

/root/one = /root/two

eval($.root.one == $.root.two)

If entries are equal

0 (false)

0 (false)

Smart URL Replacement

Instead of entering a complete address in the Request URL field of the REST Custom v2 sensor, you can only enter the protocol followed by a colon and three forward slashes (this means that you can enter either http:/// or https:///, or even a simple forward slash / as the equivalent for http:///). PRTG automatically fills in the parent device's IP Address/DNS Name in front of the third forward slash.

Whether this results in a valid URL or not depends on the IP address or Domain Name System (DNS) name of the parent device. In combination with cloning devices, you can use smart URL replacement to create many similar devices.

For example, if you create a device with the DNS name www.example.com and you add a REST Custom v2 sensor to it, you can provide values in the following ways:

  • If you enter https:/// in the Request URL field, PRTG automatically creates the URL https://www.example.com/
  • If you enter /help in the Request URL field, PRTG automatically creates the URL http://www.example.com/help
  • It is also possible to provide a port number in the Request URL field. It is taken over by the device's DNS name and is internally added, for example, https://:1616/

i_round_redSmart URL replacement does not work for sensors that run on the probe device.

Channel List

i_round_blueWhich 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

HTTP Status

The HTTP status that the requested URL returns

  • Up status: Continue, Switching Protocols, Processing, OK, Created, Accepted, Non-Authoritative Information, No Content, Reset Content, Partial Content, Multi-Status, Already Reported, IM Used
  • Warning status: Multiple Choices, Moved Permanently, Found, See Other, Not Modified, Use Proxy, Switch Proxy (deprecated), Temporary Redirect, Permanent Redirect,
  • Down status: Bad Request, Unauthorized, Payment Required, Forbidden, Not Found, Method Not Allowed, Not Acceptable, Proxy Authentication Required, Request Time-out, Conflict, Gone, Length Required, Precondition Failed, Request Entity Too Large, Request URL Too Long, Unsupported Media Type, Requested Range Not Satisfiable, Expectation Failed, I'm a teapot, Policy Not Fulfilled, There are too many connections from your internet address, Unprocessable Entity, Locked, Failed Dependency, Unordered Collection, Upgrade Required, Precondition Required, Too Many Requests, Request Header Fields Too Large, No Response, The request should be retried after doing the appropriate action, Unavailable For Legal Reasons, Internal Server Error, Not Implemented, Bad Gateway, Service Unavailable, Gateway Time-out, HTTP Version not supported, Variant Also Negotiates[13], Insufficient Storage, Loop Detected, Bandwidth Limit Exceeded, Not Extended
  • Unknown status: Unknown

i_round_blueThis channel is the primary channel by default.

[Value]

The values that a REST API returns in several channels

More

i_square_blueKNOWLEDGE BASE

What are beta sensors and how can I use them?

What security features does PRTG include?

Can I create a sensor to monitor the number of paused or unknown sensors?

 

i_square_blueMISCELLANEOUS

JSONPath Online Evaluator

JsonCons JSONPath

Stefan Gössner JSONPath