The C# questions were only shown to the developers who chose C# as one of their three primary programming languages.

Which versions of C# do you regularly use?

Almost two in every three C# developers have now moved to the latest version C#7, this is up from 44% in 2018, and 28% in 2017.

What runtimes do you regularly use?

Adoption of .NET Core is growing, although C# remains a Windows-first language: more than 90% of developers use it only on Windows.

Which technologies / frameworks do you use?

ASP.NET Core is gaining popularity alongside .NET Core.

This question was only answered by respondents who either write or use unit tests.

Which unit-testing frameworks do you regularly use?

What performance or diagnostic tools do you regularly use?

This year VSTS is on par with TFS, with both having about a 25% share. Still, 57% of developers don't use either of them.