Files with the .DIAGCAB extension contain data packed and digitally signed in the CAB format and can be used to diagnose and solve one or multiple software or device issues found in the Windows system family, from Windows Vista and Windows 7 upwards. They are used by troubleshooting tools using the WTP, which stands for Windows Troubleshooting Platform.

The files can be created both by hardware manufacturers, independent software creators, and system administrators using system tools, namely Makecab.exe and Cabarc.exe, and later digitally signed using Signtool.exe. They are often distributed using the Internet. They can be opened using the Microsoft Support Diagnostic Tool – msdt.exe.