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C# Feature - File-based app directives

File-based app directives

C# 14 expands file-based apps with new directives that configure single-file applications directly inside the .cs file.

Introduced In

This feature was introduced in C# 14. The official Microsoft Learn page for C# 14 is dated November 18, 2025 and states that C# 14 ships with .NET 10 and Visual Studio 2026.

What Was Added

#! for the shebang line used by Unix shells
#: for build-system directives used in file-based apps

Common #: directives include:

#:package
#:project
#:property
#:sdk

Example

#!/usr/bin/env dotnet
#:package Spectre.Console@*
#:property PublishAot=false

Console.WriteLine("Hello from a file-based app");

When To Use It

Use it for small utilities, demos, scripts, prototypes, or single-file tools.
Use it when a full project file would be unnecessary ceremony.

Common Pitfalls

File-based apps are intentionally lightweight, but they are not always the right structure for growing applications.
Keep the directives minimal and convert to a project when the app becomes more complex.