What is a Business Rule in ServiceNow?

What the Interviewer Wants to Hear

Business Rules are the most important server-side automation in ServiceNow. Every developer and admin needs to know the four types and their execution timing.

What Is a Business Rule?

A Business Rule is a server-side script that runs automatically when a record is displayed, inserted, updated, deleted, or queried. Think of it as an automatic trigger — you define WHEN it fires and WHAT it does.

The Four Types

• Before Business Rule: Fires BEFORE the record is saved to the database. Use it to validate data, modify field values, or abort the save entirely.

  // Example: Auto-set priority based on impact and urgency
  (function executeRule(current, previous) {
    if (current.impact == 1 && current.urgency == 1) {
      current.priority = 1; // Critical
    }
  })(current, previous);

• After Business Rule: Fires AFTER the record is successfully saved. The database write is complete. Use it for things that depend on the record existing — sending notifications, creating related records, updating other tables.

  // Example: Create a task when a change request is approved
  (function executeRule(current, previous) {
    if (current.approval.changesTo('approved')) { // Use internal value; 'approved' is the value for the approval field
      var task = new GlideRecord('change_task');
      task.initialize();
      task.change_request = current.sys_id;
      task.short_description = 'Implement: ' + current.short_description;
      task.insert();
    }
  })(current, previous);

• Async (Asynchronous) Business Rule: Fires AFTER the save but runs in the background on a separate thread. The user doesn't wait for it to finish. Use it for heavy operations — external API calls, complex calculations, bulk updates.

  // Example: Sync incident data to an external monitoring system
  (function executeRule(current, previous) {
    var rm = new sn_ws.RESTMessageV2('MonitoringSystem', 'POST');
    rm.setStringParameterNoEscape('incident_id', current.number);
    rm.execute(); // Runs in background — user doesn't wait
  })(current, previous);

• Display Business Rule: Fires when a form is loaded (displayed) to the user. Does NOT run on list views, imports, or web service calls. Use it to calculate display-only values or pass data to client scripts via the g_scratchpad object.

  // Example: Show a warning message when a VIP's incident is opened
  (function executeRule(current, previous) {
    if (current.caller_id.vip == true) {
      g_scratchpad.isVIP = true; // Pass to client script
    }
  })(current, previous);

Execution Order

// When a user clicks 'Save' on an incident form:
// 1. Client Script (onSubmit) — browser validates
// 2. Data sent to server
// 3. BEFORE Business Rules — server validates/modifies
// 4. DATABASE WRITE — record saved
// 5. AFTER Business Rules — post-save logic
// 6. ASYNC Business Rules — queued for background execution
//
// When a user OPENS a form:
// 1. Database read
// 2. DISPLAY Business Rules — prepare display data
// 3. Form renders in browser
// 4. Client Script (onLoad) — browser-side setup