Debugging ServiceNow Scripts: gs.log, gs.debug, and the Script Debugger

gs.log() — the basics

gs.log() writes to the System Log (System > System Log > All). This is your first line of debugging for server-side scripts:

gs.log('Value of state: ' + current.getValue('state'));
gs.log('Record sys_id: ' + current.sys_id);

View logs at System > System Log > All and filter by Source (usually the script name) or message content.

Log levels

gs.info('Normal operation message');
gs.warn('Something unexpected but non-fatal');
gs.error('Something failed — check this');

In production instances, debug logs are suppressed. Use gs.info() or gs.log() for messages you want to see in production.

gs.debug() with session debug

Turn on session-level debug logging at System Diagnostics > Session Debug > Log. Then gs.debug() messages appear in the session log — useful for tracing execution flow without cluttering the system log.

The Script Background page

Navigate to System Definition > Scripts - Background. You can run any server-side JavaScript here interactively and see output immediately. Invaluable for testing logic before putting it in a Business Rule:

var gr = new GlideRecord('incident');
gr.addEncodedQuery('active=true^state=1');
gr.setLimit(5);
gr.query();
while (gr.next()) {
    gs.log(gr.number + ': ' + gr.short_description);
}

The Script Debugger

The interactive Script Debugger works like a real IDE debugger — set breakpoints, step through code, inspect variable values. Access it at System Diagnostics > Script Debugger.

To use it: open the debugger, check "All scripts" or set specific filters, then trigger the script (save a record, load a form, etc.). Execution pauses at breakpoints and you can inspect the call stack.

Try/catch for graceful error capture

try {
    var gr = new GlideRecord('incident');
    gr.get(sys_id);
    // ... do something
} catch (e) {
    gs.error('Error in MyScript: ' + e.message + ' | Stack: ' + e.stack);
}

Checking if a query returned results

var gr = new GlideRecord('incident');
gr.addQuery('number', 'INC0000001');
gr.query();
if (!gr.next()) {
    gs.warn('No record found for INC0000001');
    return;
}