<%NUMBERING1%>.<%NUMBERING2%>.<%NUMBERING3%> PRTG Manual: Define Lookups

PRTG uses lookups for some sensor types and for some sensors with custom channels. In general, lookups make data more human friendly because they map status values as returned by a device (usually integers) to more informative expressions in words that show you the status of a monitored device as a clear message.

Additionally, lookups can also define the sensor status that will be shown in correlation with certain status codes, just like sensor channel limits can define a sensor status, too. For example, for a printer, PRTG can show a sensor in a yellow Warning status with channel values, provided by lookups, like "Toner Low" instead of simple status codes, like "1".

You can customize lookups individually and define your own texts that a sensor channel can show. See the section Customizing Lookups below.

icon-i-round-redIf a channel uses lookups, we strongly recommend that you control the sensor status only via the lookup definition and not use channel limits! See also section Sensor Channels Settings.

icon-i-roundLookups do not change data in the PRTG database, but they merely change the way sensor channels are shown. Any change to lookup definition files will apply to historic data as well as to live data.

icon-i-roundSome exceptions apply to the SNMP Custom String Lookup Sensor that basically does an "inverse lookup". It does not map an integer to a text message but looks only for matching strings in the lookup definition and shows a status based on this text value.

icon-prtg-on-demandCustomizing lookups is not possible for PRTG in the cloud instances.

Requirement: Channel Unit "Custom"

All sensor channels with enabled Value Lookup need to use the channel Unit "Custom". For details, refer to the section Sensor Channels Settings.

icon-i-redThere are sensors that provide the unit Value Lookup for channels in their sensor settings. Do not use the "custom" unit for channels of these sensors if you want to use lookups! This would result in malfunctioning lookup channels. For the following sensor types, choose the unit Value Lookup in the sensor settings and select your lookup file directly when adding the sensor:

Visualization of Lookup Channels

PRTG can display gauges or switches for channels which use lookups. We recommend that you stay below 120 lookup values to display informative gauges for primary channels. Non-primary channels have an upper limit of around 40 lookup values for gauges.

icon-i-roundThe various states displayed in gauges always follow the clockwise order Up (green) < Warning (yellow) < Down (red) < Unknown (Gray / Black).

A Gauge Showing the Status of a Lookup Channel

A Gauge Showing the Status of a Lookup Channel

A Switch Showing the Status of a Boolean Lookup Channel

A Switch Showing the Status of a Boolean Lookup Channel

Lookups Directory and Format

Lookups are defined in XML format in files ending in .ovl. PRTG's standard lookup files are located in the PRTG program directory in the \lookups subfolder. These files are maintained by PRTG itself. In each of the files lookups are defined for one or more sensors. Furthermore, the lookups folder contains the \custom subfolder to store your customized lookups.

The files follow a basic principle. For each numeric value you can define:

  • A message that the sensor will look up and show instead of the numerical value
  • The status that the sensor will show

icon-i-roundUse the SNMP Custom String Lookup Sensor to map a string into a corresponding status. Please use the lookup type SingleInt for this purpose.

icon-prtg-on-demandYou cannot access this directory on PRTG in the cloud instances.


The following code illustrates the lookup definition for the toner status of the SNMP HP LaserJet Hardware sensor:

<?xml version="1.0" encoding="UTF-8"?>
<ValueLookup id="oid.paessler.hplaserjet.tonerstatus" desiredValue="1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="PaeValueLookup.xsd">
         <SingleInt state="Ok" value="0">Toner Okay</SingleInt>
         <SingleInt state="Warning" value="1">Toner Low</SingleInt>
         <SingleInt state="Error" value="2">No Toner Cartridge Loaded</SingleInt>


The schema in the example provides an insight how lookups are defined:

  • The <?xml> tag in the first line defines the content as XML.
  • The <ValueLookup> tag in the second line contains:
    • The ID which is shown in the Sensor Channels Settings.
    • The desiredValue attribute contains the value which is used for the calculation of the "Coverage". In this example, 1 is defined as desired value.
    • The xsi attributes refer to PRTG's predefined XML schema definitions (which allow easy editing of lookup files with supported editors). We recommend that you use the default value.
  • Between the tags <Lookups> and </Lookups> the particular lookups for the sensor data are defined:
    • A lookup entry starts with a tag containing the type of the status value, the lookup type (in this example, this is always <SingleInt>).
    • Separated by whitespace, the state attribute defines the status the sensor will show. Allowed values are: Ok, Warning, Error, and None ("None" does not trigger a status change).
    • The value attribute defines which numeric value will trigger the lookup. This is the value that PRTG will receive from the device.
    • The text defines the substitution text that is shown instead of the value. For example, this can be a status message.
  • The same way all other possible lookups are defined. The lookup definitions are closed by the tag </Lookups>. The file closes with </ValueLookup>.

In our example, the lookup file will have the following effect:

Value as Reported from HP Printer

Value Shown in PRTG (Sensor Channel)

Sensor Status Shown by PRTG


Toner Okay




Toner Low




No Toner Cartridge Loaded



The XML Schema

An exemplary schema of the XML files containing the lookup definitions can be sketched like this:

<?xml version="1.0" encoding="UTF-8"?>
<ValueLookup id="..." desiredValue="..." undefinedState="..." xmlns="..." xsi="...">
         <SingleInt state="..." value="...">status text</SingleInt>
         <Boolean state="..." value="...">status text</Boolean>
         <BitField state="..." value="...">status text</BitField>
         <Range state="..." from="..." to="...">status text</Range>
         [several other lookup definitions]




Attributes, Value Assignment, and Content


This is the XML declaration. Every XML file begins with it.

  • version and encoding are "1.0" resp. "UTF-8"
  • content: <ValueLookup>contentValueLookup</ValueLookup>


Defines the ID of the channel, what desiredValue is used, the status for undefined values (undefinedState), and links to PRTG's predefined schema definitions, which allow editing of lookup files with supported editors.

  • id: Specifies how the name of the lookup file is shown in the Sensor Channels Settings.
  • desiredValue: Please see below.
  • undefinedState: Optionally define a status for values that are not defined in the lookup file. If the target device returns a value that is not included in the lookup definition, the sensor will show this status (Ok, Warning, Error, or None) with an according message. Without a definition of "undefinedState", the sensor will only show the returned value.
  • xmlns:xsi/xsi: refers to predefined XML schema definition
  • contentValueLookup: lookup definitions


Defines the particular lookups for the sensor data.

  • contentLookups: one or more lookup entries, see below

status text

status text

status text

status text

Each element defines one lookup entry. There can be one or more entries in this format. SingleInt, Boolean, BitField, and Range are lookup types.

  • state: defines the state the sensor will show; allowed values: Ok, Warning, Error, None
  • value: defines the value which triggers the lookup. Please enter an integer value.
    icon-i-round-redRange needs always both values "from" and "to".
  • status text: defines a status text that will be used as substitution text and shown instead the integer value. For example, a status message.

icon-i-round-redThe SNMP Custom String Lookup Sensor maps the status text into one of the given states. Please use SingleInt for this sensor.

Because all the XML files containing lookup definitions are delivered in a pre-given schema as indicated above, you can customize lookups accordingly.

Customizing Lookups

If you want to change the status definitions of a specific sensor channel, you basically have to do the following:

  1. Find out the (file) name of the lookup file in the settings of the sensor channel you want to change the behavior for.
  2. From the PRTG program directory subfolder \lookups, copy this file into the \lookups\custom subfolder (ensure you do not change the file name!).
  3. Change the duplicated file as you like. See the example below.

icon-prtg-on-demandThis feature is not available in PRTG in the cloud.

All default lookup files are located in the \lookups subfolder in the PRTG program directory. To customize existing lookups, copy the desired lookup file from the lookups folder to the \lookups\custom subfolder or create a new .ovl file there. When using the same ID in the ValueLookup tag, the files in the \lookups\custom folder will have a higher priority than the original files in the \lookups folder. This way, PRTG handles your customizations preferably instead of the original lookup settings. If you want to use custom lookup definitions in addition to the existing lookups, define a new ID in the lookup file which is not used by another lookup file. PRTG identifies lookup definitions via this ID, it does not use the file name.

Open the file with an XML or text editor and adjust the lookups to your personal preferences. You can define your own messages as well as you can customize sensor states for the particular return values. For example, if you do not want show an "Error" (a sensor Down status) for the return value "2" but only a warning, then you can replace "Error" with "Warning".

icon-i-roundThe possible states are given in the LookupState.xsd file in the custom directory. Following the schema of the XML files that are delivered with PRTG enables you to edit the lookups in a safe way.

icon-i-roundIf you imported an oidlib file that contains lookups (you can see this in section Lookup in the MIB Importer), you can define your own sensor states for returning values. If you add an SNMP Library Sensor using this oidlib, PRTG will create a lookup definition file using the lookupname of the chosen library as id parameter. Override this lookup definition with your own custom lookup as described in this section. This is important because lookups that are added via an oidlib will not contain any state definitions and result in a Warning status of the sensor by default because of the entry undefinedState="Warning".

icon-i-roundIf you use an SNMP Custom String Lookup Sensor, you can create a new custom lookup definition in the \lookups\custom directory with the expected return values. In this case, use the lookupname of the chosen library as id parameter to override the lookups from the oidlib file.

icon-i-round-redWhen you save an edited lookup, make sure that it is saved as an .ovl file. Otherwise, the lookup might accidentally be saved as a .txt file and might not be loaded.

Example for Lookups Customization

For example (just for illustration purposes), imagine you would like

  1. to have the status "Warning" for all undefined values that the target device might return,
  2. to change the status for the return value "2" from "Down" to "Warning",
  3. and to add the status "None" to the example above.

Then do the following:

  • Copy the file oid.paessler.hplaserjet.tonerstatus to the \lookups\custom subfolder of your PRTG installation.
  • Open this file with an editor.
  • Leave the ID value unchanged to prioritize the customized lookup to the original file.
  • Insert the status definition for undefined values into the ValueLookup element: undefinedState="Warning"
  • Replace "Error" with "Warning" for value "2".
  • Add a a "SingleInt" element with status "None" for the (hypothetical) return value "3".
  • Save the file and reload the custom lookup folder in PRTG.

The customized lookup file will finally look like this:

<?xml version="1.0" encoding="UTF-8"?>
<ValueLookup id="oid.paessler.hplaserjet.tonerstatus" desiredValue="1" undefinedState="Warning" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="PaeValueLookup.xsd">
         <SingleInt state="Ok" value="0">Toner Okay</SingleInt>
         <SingleInt state="Warning" value="1">Toner Low</SingleInt>
         <SingleInt state="Warning" value="2">No Toner Cartridge Loaded</SingleInt>
         <SingleInt state="None" value="3">Unknown status of toner</SingleInt>

icon-book-arrowsSee also SNMP Custom String Lookup Sensor—Example for a lookup definition that maps a string value to a sensor status.

desiredValue Attribute

It is necessary to define a desiredValue in the lookup files. The desiredValue corresponds to a status value triggering a lookup. PRTG calculates the percentage of time this specific state has been monitored. The result is displayed for all data tables and graphs that show averaged values.

Considering the example above where the desiredValue is "1", PRTG will calculate the percentage of time the toner status has been "Warning". If in a time span of five minutes four of five sensor scans returned a "Warning" status, PRTG would show an average of 80% for this time span, because in 80% of the time the sensor showed a "Warning".

Lookup Types: SingleInt, Boolean, BitField, Range

Besides the lookup type SingleInt as seen above, there are three other lookup types: Boolean, BitField and Range. Using these types you can define lookup values beyond simple integers.

Lookup Type




Uses an integer to define a lookup for one status value.


icon-i-round-redThe full 32-bit integer range is supported.


Uses 0 or 1 to define a lookup for two different status values.



Uses a bitfield for multiple status values.

Only use it if you have basic knowledge about bitmasks. Please see the section More below for a general introduction.

icon-i-round-redEvery value has to equal a power of two (for example, 1, 2, 4, 8, 16, 32, 64, etc.).

icon-i-round-redThe SNMP Custom String Lookup Sensor does not support BitFields.


Uses an inter range from-to to define a lookup for several status values.

from="int" to="int"

icon-i-round-redUsing ranges, the parameters "from" and "to" always have to be defined. If you want to query only one single value in a range file, this value must be set as parameter for "from" and "to" (for example, from="2" to="2").

icon-i-round-redThe SNMP Custom String Lookup Sensor does not support ranges.

icon-i-round-redThe full 32-bit integer range is supported.

icon-i-roundYou can use only one kind of lookup type in one lookup file. This means, only or SingleInts, or Boolean, or BitField, or Ranges. Different lookup types in one file are not allowed.

Define Lookup Files in Sensor Channel Settings

For each sensor with a custom channel, you can define a lookup file to use with the option Value Lookup in the sensor channel settings. This option is visible for many SNMP sensors, some application sensors, and always for the following sensor types:

icon-book-arrowsFor details, see section Sensor Channel Settings.

Loading Lookups

You can (re)load the defined lookups in the custom folder by clicking the Load Lookups button in the PRTG web interface under Setup | System Administration | Administrative Tools.

icon-i-blueA sensor whose lookup file you have modified and reloaded will not re-evaluate this lookup before the next sensor scan. For sensors with large scanning intervals, use the Check Now option from the context menu to immediately apply the new lookup definition and to avoid an incorrect sensor status.

Debugging—What will happen if...?

  • A return value is defined in the lookups that never will be returned by a device because the value is not assigned: The value will never be triggered, so PRTG simply ignores this entry.
  • PRTG receives a return value that is not defined for lookups: No substitution message can be found. PRTG will just show the return value. You can optionally define a status for unknown values with a definition of undefinedState in the ValueLookup element (see section Define Lookups—The XML Schema above).
  • Different lookup types are in one lookup file: This is not allowed and PRTG will discard this lookup definition. If you use miscellaneous lookup types in one file, for example, ranges and singleInts together, the PRTG system will create a ticket when loading lookups or restarting the PRTG server with the following error message: Value lookup file "[...]" could not be loaded ("" is not a valid integer value)".
  • Incorrect XML code: PRTG will create a new ticket when loading lookups or restarting the PRTG server with a corresponding error message and discard this lookups definition.
  • A lookup file has a file ending other than .ovl: The file will not be loaded.


Video Tutorial: How to configure lookups in PRTG Network Monitor

Wikipedia: Masks (computing)


Advanced Topics

Keywords: Lookups,SNMP,SNMP Lookups,Value Mapping,Value Mapping Lookups