1# KQL Query Reference
2 
3Essential Kusto Query Language (KQL) queries for diagnosing Azure application issues.
4 
5## Prerequisites
6 
7- Application Insights or Log Analytics workspace configured
8- Diagnostic settings enabled on Azure resources
9 
10---
11 
12## Recent Errors
13 
14```kql
15// Recent errors
16AppExceptions
17| where TimeGenerated > ago(1h)
18| project TimeGenerated, Message, StackTrace
19| order by TimeGenerated desc
20```
21 
22## Failed Requests
23 
24```kql
25// Failed requests
26AppRequests
27| where Success == false
28| where TimeGenerated > ago(1h)
29| summarize count() by Name, ResultCode
30| order by count_ desc
31```
32 
33## Slow Requests
34 
35```kql
36// Slow requests
37AppRequests
38| where TimeGenerated > ago(1h)
39| where DurationMs > 5000
40| project TimeGenerated, Name, DurationMs
41| order by DurationMs desc
42```
43 
44## Dependency Failures
45 
46```kql
47// Dependency failures
48AppDependencies
49| where Success == false
50| where TimeGenerated > ago(1h)
51| summarize count() by Name, ResultCode, Target
52```
53 
54---
55 
56## Tips
57 
58- Always include time filter: `TimeGenerated > ago(Xh)`
59- Limit results with `take 50` for large datasets
60- Use `summarize` to aggregate data before analyzing
61 
62## More Resources
63 
64- [KQL Quick Reference](https://learn.microsoft.com/azure/data-explorer/kql-quick-reference)
65- [Application Insights Queries](https://learn.microsoft.com/azure/azure-monitor/logs/queries)
66