PRTG Manual: REST Custom v2 Sensor

Enabled Beta Sensors experimental feature

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

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

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.

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

Channel #x JSONPath/XPath

Enter the JSONPath or XPath that you want to monitor.

JSONPath example:

$.sensorxref[0].totalsens

If the JSONPath points to a boolean, the sensor translates TRUE as 1 and FALSE as 0.

XPath example:

/bookstore/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.

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?

Channel #x Custom Unit

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

Channel #x 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.
  This 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.

Sensor Name

Enter a name to identify the sensor.

Parent Tags

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

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:

• rest

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 ().

Request URL

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

JSON REST API endpoint URL example:

https://mycompany.com/api/table.json?id=1&passhash=<passhash>&username=<username>&content=sensorxref&
noraw=1&filter_basetype=probe&columns=totalsens=textraw,upsens=textraw,
downsens=textraw,partialdownsens=textraw,warnsens=textraw,pausedsens=textraw,
unusualsens=textraw,undefinedsens=textraw,downacksens=textraw

XML REST API endpoint URL example:

https://mycompany.com/api/table.xml?sortby=year

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.

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.

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

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

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.

Content Type

Select the type of the content that the sensor queries. Choose between:

• 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:

$..prtg-version

XPath example:

/bookstore/book[1]/title

Channel #x JSONPath/XPath

Enter the JSONPath or XPath that you want to monitor.

JSONPath example:

$.sensorxref[0].totalsens

If the JSONPath points to a boolean, the sensor translates TRUE as 1 and FALSE as 0.

XPath example:

/bookstore/book[1]/year

Channel #x Type

Shows the value type that the channel displays.

PRTG 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.

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

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.

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.

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.

{
"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
     }
   }
 }
 ]
}

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 (-) are not supported.
• [<key>] must only contain a number or a quoted string.

Example

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 (*).

• .*
• [*]

Example

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 (..).

Example

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

$..tx_bytes

Union

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

Example

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.

Example

This expression matches 63685865 in the example above:

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

Current

The @ symbol matches the current element.

Example

This expression matches 40.085321 and 55.294975 in the example above and can be used to receive a percentage value:

$.devices[1].networks.a.["rx_bytes","tx_bytes"](@/100000000*100)

Filter

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

Example

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

Script

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>, ...]
• Objects: {<expression>:<expression>, <expression>:<expression>, ...}
• Conditionals: <condition> ? <expression> : <expression>

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 in percent.

HTTP Status

The HTTP status that the requested URL returns

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.