Which compiler is used in ASP.NET?

Roslyn is the name of the compiler used by .NET Framework.

In ASP.NET, the compiler used depends on the version of ASP.NET being used:

  1. ASP.NET Web Forms (Traditional ASP.NET): In this case, the C# or VB.NET code is typically compiled at runtime using the ASP.NET runtime compiler, which compiles the code into Intermediate Language (IL) and then further into native code by the Just-In-Time (JIT) compiler.
  2. ASP.NET Core: ASP.NET Core applications can use either the .NET Core CLR or the .NET Framework CLR. The code is compiled ahead of time (AOT) or just-in-time (JIT) depending on the platform and deployment configuration. Additionally, ASP.NET Core supports cross-platform development, meaning it can run on Windows, Linux, or macOS.

So, the correct answer would be that in ASP.NET, the C# or VB.NET code is compiled at runtime by the ASP.NET runtime compiler, and the specific compiler used can vary based on the version and configuration of ASP.NET being used.