.CSX File Extension

Developer file written in Visual C# Script, a C# API developed by Microsoft under the codename The Roslyn Project; used for developing components in C# that can run on-demand as scripts with the Roslyn framework.

The Roslyn program that runs CSX files as scripts is named rcsi.exe. This program is part of the Roslyn package, which can be installed using the NuGet service in Microsoft Visual Studio.