Workers

Write Cloudflare Workers in C# compiled to native JavaScript.

using Workers;

public static class Worker
{
    [Fetch]
    public static Response Handle(
        Request request,
        Env env,
        Context context)
    {
        return Response.Text("Hello from C#!");
    }
}

Getting started

Add the package to a .NET project:

dotnet add package Workers

Publish the Worker:

dotnet publish -c Release

The generated dist/worker.js is a native ES module ready for Wrangler. Configure bindings, routes, and other deployment settings in your Wrangler configuration.

ASP.NET Minimal APIs

The same package can compile familiar ASP.NET Minimal API projects directly to native Worker routing:

var builder = WebApplication.CreateSlimBuilder(args);
var app = builder.Build();

app.MapGet("/users/{id:int}", (int id) => Results.Ok(new { id }));
app.MapPost("/users", (CreateUser user) => Results.Created("/users/1", user));

app.Run();

Use the Microsoft.NET.Sdk.Web SDK or reference Microsoft.AspNetCore.App. Routing, parameter binding, JSON bodies, common results, and source-declared handlers are compiled away; ASP.NET and Kestrel are not included in the Worker. Unsupported middleware or dependency-injection features produce a compiler diagnostic.

Workers API

The package provides a focused C# API for Workers requests, responses, events, bindings, Durable Objects, queues, KV, R2, D1, Cache, WebSockets, TCP sockets, email, and other platform features.

[Fetch]
public static async Task<Response> Handle(
    Request request,
    Env env,
    Context context)
{
    var users = env.Kv("USERS");
    var user = await users.GetJsonAsync<User>("current");

    if (user is null)
        return Response.Text("User not found", status: 404);

    return Response.Json(user);
}

Familiar C# APIs such as Task, Console, Guid, and DateTimeOffset are supported where they map cleanly to the Workers runtime. Unsupported language or .NET features produce a compiler diagnostic instead of shipping a compatibility runtime.

Version 0.3

Versions through 0.2.0 ran .NET on WebAssembly and supported managed assemblies and compatible NuGet packages. Every Worker also had to ship and initialize the .NET runtime, framework files, and a JavaScript interoperability adapter, resulting in large bundles, slow startup, and high CPU usage.

Starting with 0.3.0, Workers compiles a focused C# profile directly to native JavaScript. Removing the runtime and interoperability layer reduces generated output by up to 99%. In a basic-response baseline, output falls from approximately 4.9 MB to about 200 bytes raw. This is a breaking change: arbitrary NuGet packages and the complete .NET BCL are no longer supported.

Examples

See the examples directory for complete Workers covering HTTP, storage, queues, scheduled events, and other platform APIs.