SharpForge

A complete C# toolchain that runs in the browser.
Compiler, .NET-compatible IL, managed runtime, debugger, WinUI-style UI framework, visual designer and a Visual Studio-style IDE — written in JavaScript, with no server and no install.

Open SharpForge Studio →  ·  Quick start  ·  Architecture  ·  Status  ·  Roadmap

Work in progress. SharpForge is a development preview on the way to full C#, CLR, .NET BCL, WinUI and Visual Studio parity. Features below are marked Available, Preview, WIP or Planned. A program compiling and running here is not yet a guarantee that it behaves exactly as it does on .NET; see Status.

What is SharpForge?

SharpForge lets you write, build, run, debug and design C# applications entirely inside a web page.

• Write C# in an editor with IntelliSense, navigation, refactorings and Visual Studio, VS Code, Vim, Emacs or Sublime key bindings.
• Build it with a C# compiler that emits real ECMA-335 assemblies (.dll) and Portable PDBs that the .NET runtime also loads.
• Run it on a managed runtime with its own garbage collector, task scheduler and base class library — in a Web Worker, in Node.js, or from the command line.
• Debug it with breakpoints, stepping, watches, call stacks, reverse stepping, IL-level debugging and Hot Reload.
• Design user interfaces with WinUI-shaped controls and a visual designer that edits your C# in both directions.
• Ship nothing to a server: the whole product is a static site, and it also works as a single offline HTML file.

Features

Language and compiler

Runtime

UI framework and designer

IDE (SharpForge Studio)

Architecture

SharpForge is a set of small, independent packages composed into three hosts: the Studio IDE, a command-line tool, and standalone HTML output.

What makes it unusual: the whole .NET-style stack is written in JavaScript. There is no C++ runtime, no Roslyn and no server behind it.

The product has no npm runtime dependencies. Python is used only for the browser test suites. Dashed boxes in the diagram are planned (Rust runtime) or external (.NET runtime, shown because it loads the same assemblies SharpForge emits).

How a program flows through it. Source text is parsed into a lossless syntax tree, bound into a typed semantic model, lowered (closures, iterators, async and patterns become plain classes and control flow) and emitted twice: as compact managed bytecode for the debugging VM, and as a standard ECMA-335 assembly that the CIL interpreter — or a real .NET runtime — can load. The runtime executes it inside a Web Worker with its own heap, garbage collector and scheduler; framework calls reach the base class library, the network layer (denied unless an origin is explicitly granted) and the WinUI layer, which renders through WebGPU, Canvas or the DOM.

Packages

Every package under packages/ is published as @sharpforge/<name> and can be used on its own; see Embedding. Design details are in Architecture.

Quick start

In the browser — open https://wieslawsoltes.github.io/SharpForge/. Pick an example from Examples, press Start, set a breakpoint, or open Designer.

Locally — requires Node.js 22 or later; there are no runtime dependencies.

git clone https://github.com/wieslawsoltes/SharpForge.git
cd SharpForge
npm ci
npm start          # builds and serves Studio at http://127.0.0.1:4173

From the command line

node apps/cli/main.js run Program.cs                 # compile and run
node apps/cli/main.js compile Program.cs -o app.dll  # emit a .NET assembly
node apps/cli/main.js exec app.dll                   # run an assembly
node apps/cli/main.js compile Program.cs --format dotnet -o app.dll && dotnet app.dll
                                                     # a real .NET assembly, bound against the installed
                                                     # SDK's reference pack, run by the .NET runtime
node apps/cli/main.js decompile library.dll          # inspect any assembly
node apps/cli/main.js new console --name Hello -o ./Hello
node apps/cli/main.js --help

A first program

using System;

var total = 0;
foreach (var n in new[] { 1, 2, 3, 4 })
    total += n * n;

Console.WriteLine($"Sum of squares: {total}");

A first window

using Microsoft.UI.Xaml;
using Microsoft.UI.Xaml.Controls;

class Program
{
    static TextBlock label;
    static int count;

    static void OnClick(object sender, RoutedEventArgs args)
    {
        count++;
        label.Text = $"Clicked {count} times";
    }

    static void Main()
    {
        label = new TextBlock { Text = "Clicked 0 times" };
        var button = new Button { Content = "Click me" };
        button.Click += OnClick;

        var panel = new StackPanel { Spacing = 12 };
        panel.Children.Add(label);
        panel.Children.Add(button);

        var window = new Window { Title = "Hello SharpForge", Content = panel };
        window.Activate();
    }
}

Screenshots

Status

SharpForge 0.14 is a development preview. It implements a documented, growing subset of C#, the CLR, the .NET base class library and WinUI. The goal is full parity; the work is tracked in the open.

The full programme, with every epic and task, is on the Portfolio board and in the tracking issue.

Known limits today. Not every valid C# program compiles or runs; programs using features the runtime cannot execute yet are rejected with a clear diagnostic rather than miscompiled. The base class library is a subset and can differ from .NET in formatting and culture behaviour. The WinUI layer follows WinUI's API shape but is not the Windows App SDK. See Compatibility.

Security model

• Everything runs locally in your browser; your code is not uploaded.
• Managed programs cannot reach the network unless you grant an exact origin, and grants are never restored from saved workspaces.
• The site ships with a strict Content-Security-Policy and uses no eval.
• Native builds run only through an explicitly trusted local host.

Documentation

Development

npm run check            # syntax check
npm run check:structure  # file-size and structure gate
npm test                 # unit and integration tests
npm run build            # build Studio into dist/
npm run standalone       # build the single-file SharpForge-standalone.html

Browser tests use Playwright (pip install -r tests/requirements.txt, then npm run test:browser).

Contributing

Contributions are welcome. Read CONTRIBUTING.md first — it covers architecture rules, code quality, file-size limits, performance expectations, testing and the pull-request workflow. Work items live on the project boards; pick one marked Ready.

License

MIT. Third-party notices are in THIRD_PARTY_NOTICES.md.

SharpForge is an independent project. It is not affiliated with or endorsed by Microsoft; C#, .NET, Visual Studio, WinUI and Windows are trademarks of Microsoft Corporation.