KQL Fundamentals – Extent

Level: Beginner | Reading time: 5 minutes

Let’s continue our series on KQL with a focus on Cyber Security. Let’s talk today about how to use the Extent command. Other posts can be seen in our KQL category.

You can use the extent command to create new calculated columns and append them to the result set, this adds a new column to the input result set that will appear as the last column on the right side of the search.


T| extend [ColumnName | (ColumnName[, …])=Expression [, …]

It is also possible to use extend on multiple columns at the same time.

| where TimeGenerated > ago(7d)
| extend severityOrder = case (
AlertSeverity == "High", 3,
AlertSeverity == "Medium", 2,
AlertSeverity == "Low", 1,
AlertSeverity == "Informational", 0,

Let’s see how this would apply to a Microsoft Sentinel detection rule. Here, we use extend to create two new columns HTTP_Status_Code and Domain:

let timeframe = 1d;

let DomainList = dynamic(["tor2web.org", "tor2web.com"]);

| where TimeGenerated >= ago(timeframe)
| where ProcessName contains "squid"
| extend
HTTP_Status_Code = extract("(TCP_(([A-Z]+)…-9]{3}))",8,SyslogMessage),
Domain = extract("(([A-Z]+ [a-z]{4…Z]+ )([^ :\/]*))",3,SyslogMessage)
| where HTTP_Status_Code == "200"
| where Domain contains "."
| where Domain has_any (DomainList)


Use the extend operator – Learn | Microsoft Docs

extend operator – Azure Data Explorer | Microsoft Docs

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Tiago Souza

Tiago Souza

Security Technical Specialist
Cyber Security Technical Specialist at Microsoft | Cloud Security & Threat Protection | Blog content creator at CyberGeeks.Cloud - https://linktr.ee/tiagovf