What is a Data Lookup Rule in ServiceNow?

[Mummadisetty]

I would like to understand the concept of Data Lookup Rules in ServiceNow with a practical example.

How are they configured, and how do they automatically set field values on a form?

Additionally, what are best practices for using them in production environments.

[GlideFather]

Hi @Mummadisetty,

the easiest example to understand is calculation of Priority. That field is read-only and changes as per the values in Impact and Urgency.

Urgency 1 + Impact 1 = Priority 1,

Urgency 2 + Impact 2 = Priority 2,

etc...

https://yourinstance.service-now.com/dl_u_priority_list.do

You can check it in the lookup definitions

https://yourinstance.service-now.com/dl_definition_list.do

[Dr Atul G- LNG]

Hi @Mummadisetty 

https://youtu.be/K7L3n3AUYmE

My video will be helpful

https://www.servicenow.com/docs/r/washingtondc/application-development/table-administration-and-data...

[yashkamde]

Hello @Mummadisetty ,

Data Lookup Rules are a no‑code automation feature in ServiceNow that allow administrators to automatically set field values on a form based on defined conditions. They’re essentially a way to replace small client scripts or business rules with a simpler, maintainable configuration.

For Ex : In Incident table Priority matrix i.e how on the basis of impact x Urgency Priority is set..
Below I implemented this in custom table :

For this you have to make a record in Data look definition (Navigate through application navigator) :

Also Matcher table should be custom which is extended by Data lookup matcher rules table and set the choices their :

If my response helped mark as helpful and accept the solution.

[Tanushree Maiti · Accepted solution]

Data Lookup Rules in ServiceNow allow administrators to define logic that automatically sets field values on a form based on the values of other fields, without writing code. This "low-code" approach uses a Matcher Table (containing predefined combinations) to determine values for Setter Fields on a Source Table.

How Data Lookup Rules Work
The system executes a query against a custom lookup table to find a matching row. If a match is found, it returns the values defined in the "setter" fields to the target record.

Source Table: The table where you want fields to be automatically updated (e.g., Incident, Change, or a Custom Table).
Matcher Table: A custom table that extends the Data Lookup Matcher Rules (dl_matcher) table. It stores the "logic" as data rows.
Matcher Fields: The "If" conditions (e.g., If Impact is 'High' and Urgency is 'High'...).
Setter Fields: The "Then" actions (...then set Priority to '1 - Critical').

Practical Example: VIP Assignment Rule
A common community example is automatically assigning a ticket and setting its priority when a VIP Caller is selected.

Create a Matcher Table: Create a new table (e.g., u_vip_lookup) that extends dl_matcher.
Define Fields in Matcher Table:
Matcher Field: u_caller (Reference to User table).
Setter Fields: u_priority (Integer) and u_assignment_group (Reference to Group table).
Add Data Rows:
Row 1: Caller: Fred Luddy | Priority: 1 | Group: VIP Support.
Row 2: Caller: Beth Anglin | Priority: 2 | Group: VIP Issues.
Create Data Lookup Definition: Navigate to System Policy > Rules > Data Lookup Definitions and link the Incident table (Source) to your u_vip_lookup table (Matcher).
Result: When a technician selects "Fred Luddy" on an incident form, the Priority and Assignment Group fields immediately auto-populate based on your table rows.