A CSX file is a C# script file primarily used by the Roslyn compiler (the .NET Compiler Platform) and various scripting engines like scriptcs or dotnet-script. Unlike standard C# source files with the .cs extension, which are typically part of a structured project and must be compiled into an assembly before execution, CSX files are designed for immediate execution and scripting purposes. They allow developers to write C# code that can be run directly without the boilerplate of a full project, such as namespace declarations or a static Main method. CSX files support top-level statements and special directives like #r for referencing external DLLs and #load for including other script files. This format is highly popular for automation tasks, rapid prototyping, interactive coding in REPL environments, and defining build or deployment logic within the .NET ecosystem. It bridges the gap between the power of a statically typed language like C# and the flexibility of a scripting language.