KQL Query Reference

Essential Kusto Query Language (KQL) queries for diagnosing Azure application issues.

Prerequisites

• Application Insights or Log Analytics workspace configured
• Diagnostic settings enabled on Azure resources

Recent Errors

// Recent errors
AppExceptions
| where TimeGenerated > ago(1h)
| project TimeGenerated, Message, StackTrace
| order by TimeGenerated desc

Failed Requests

// Failed requests
AppRequests
| where Success == false
| where TimeGenerated > ago(1h)
| summarize count() by Name, ResultCode
| order by count_ desc

Slow Requests

// Slow requests
AppRequests
| where TimeGenerated > ago(1h)
| where DurationMs > 5000
| project TimeGenerated, Name, DurationMs
| order by DurationMs desc

Dependency Failures

// Dependency failures
AppDependencies
| where Success == false
| where TimeGenerated > ago(1h)
| summarize count() by Name, ResultCode, Target

Tips

• Always include time filter: TimeGenerated > ago(Xh)
• Limit results with take 50 for large datasets
• Use summarize to aggregate data before analyzing

More Resources

• KQL Quick Reference
• Application Insights Queries