C# file-based apps

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C# file-based applications let you run single .cs files without a .csproj project file. This feature, built on .NET 10 SDK’s file-based app support, integrates directly with Aspire’s orchestration. Use AddCSharpApp to add these lightweight apps to your AppHost alongside traditional projects, containers, and executables.

When to use file-based apps

Use file-based apps when you need to:

Prototype a service quickly without project scaffolding.
Run simple worker processes or background tasks.
Create lightweight APIs with minimal ceremony.
Experiment with Aspire integrations in a single file.

For production workloads or apps with multiple source files, use AddProject<T> with a standard .csproj project instead.

Basic usage

Call AddCSharpApp with a resource name and the relative path to a .cs file:

#pragma warning disable ASPIRECSHARPAPPS001

var builder = DistributedApplication.CreateBuilder(args);

builder.AddCSharpApp("worker", "../worker/Program.cs");

builder.Build().Run();

The path is resolved relative to the AppHost directory. You can also point to a .csproj file or a directory that contains one:

#pragma warning disable ASPIRECSHARPAPPS001

var builder = DistributedApplication.CreateBuilder(args);

// Point to a .csproj file
builder.AddCSharpApp("api", "../api/Api.csproj");

// Point to a directory containing a .csproj file
builder.AddCSharpApp("frontend", "../frontend/");

builder.Build().Run();

Resource dependencies

File-based apps integrate fully with Aspire’s resource model. You can reference other resources, configure service discovery, and set environment variables just like any other project resource:

#pragma warning disable ASPIRECSHARPAPPS001

var builder = DistributedApplication.CreateBuilder(args);

var cache = builder.AddRedis("cache");
var db = builder.AddPostgres("pg").AddDatabase("mydb");

builder.AddCSharpApp("worker", "../worker/Program.cs")
    .WithReference(cache)
    .WithReference(db)
    .WithExternalHttpEndpoints();

builder.Build().Run();

The file-based app receives connection strings and service discovery information through environment variables, exactly like projects added with AddProject<T>.

Configure options

The AddCSharpApp method accepts an optional Action<ProjectResourceOptions> parameter to configure launch settings:

#pragma warning disable ASPIRECSHARPAPPS001

var builder = DistributedApplication.CreateBuilder(args);

builder.AddCSharpApp("api", "../api/Api.cs", options =>
{
    options.LaunchProfileName = "https";
    options.ExcludeLaunchProfile = false;
    options.ExcludeKestrelEndpoints = false;
});

builder.Build().Run();

The available options are the same as those used with AddProject<T>:

Option	Description
`LaunchProfileName`	The name of the launch profile to use from launchSettings.json.
`ExcludeLaunchProfile`	When `true`, ignores launch profile settings.
`ExcludeKestrelEndpoints`	When `true`, doesn’t automatically add Kestrel endpoints.

File-based AppHost

You can also write the AppHost itself as a file-based app using the #:sdk directive:

#:sdk Aspire.AppHost.Sdk@13.1.0
#:package Aspire.Hosting.Redis@13.1.0

#pragma warning disable ASPIRECSHARPAPPS001

var builder = DistributedApplication.CreateBuilder(args);

var cache = builder.AddRedis("cache");

builder.AddCSharpApp("worker", "../worker/Program.cs")
    .WithReference(cache);

builder.Build().Run();

Use #:package directives to add NuGet package references directly in the source file instead of a .csproj.

Limitations

Since this feature is experimental, be aware of the following limitations:

Experimental status — the API is marked with [Experimental("ASPIRECSHARPAPPS001")] and may change in future releases.
Single-file only — file-based apps are limited to a single .cs file per resource.
.NET 10 SDK required — file-based app execution requires the .NET 10 SDK or later.
No deployment support — file-based apps are designed for local development scenarios.

Suppress the diagnostic

To use AddCSharpApp, suppress the ASPIRECSHARPAPPS001 diagnostic using one of these methods:

In code with a pragma directive:

#pragma warning disable ASPIRECSHARPAPPS001
builder.AddCSharpApp("worker", "../worker/Program.cs");
#pragma warning restore ASPIRECSHARPAPPS001

In your project file with NoWarn:

<PropertyGroup>
    <NoWarn>$(NoWarn);ASPIRECSHARPAPPS001</NoWarn>
</PropertyGroup>

In an .editorconfig file:

[*.{cs,vb}]
dotnet_diagnostic.ASPIRECSHARPAPPS001.severity = none