What is Microsoft Support Diagnostic Tool?

It's a tool which is used by Microsoft Support to diagnose Windows problem.You can use the Microsoft Support Diagnostic Tool to collect information about problems you might be experiencing with your computer.

The tool can help Microsoft Support solve problems more efficiently than by diagnosing over the phone or by using e-mail.

How To launch Microsoft Support Diagnostic Tool

In the Start Search type in MSDT and hit the Enter key. You can also launch the same from Run menu.

How shall I get the Passkey?

Contact Microsoft Support for your problem. To use the tool, follow the instructions from Microsoft Support and answers accordingly. The support professional of Microsoft will provide the passkey as well as an incident number to enter into the tool to identify your information. You may need to download additional diagnostic tools. The tool will run and save the results which you can send to Microsoft.

Can I run MSDT if there is no internet connection?

Yes. This package is called Offline package. It will generate a CAB file with diagnostic information which you can send to Microsoft.

[Note: This article is also applicable for Windows 10 Creator Update]