A library of Embeddable TypeScript console for .NET applications.

Duets lets you drop a fully-featured TypeScript REPL into **any** .NET application — desktop, mobile (iOS / Android / MAUI), game engines (Unity, Godot), servers, and everything in between. Use it for live debugging, runtime scripting, or as an in-app scripting language.

Features

• TypeScript transpilation & execution — powered by Jint running Babel (default) or the official TypeScript compiler in-process. No Node.js required.
• Auto-generated type declarations — expose .NET types to the editor and get IntelliSense-style completions via automatically generated .d.ts files. Attach .NET XML documentation (JsDocProviders) to include prose summaries, @param, and @returns annotations in the editor.
• Browser debug pad (DuetsPad) — a Monaco Editor frontend served over a built-in HTTP server, with an output canvas, execution timeline, and SSE-based live type declaration updates.
• Zero heavy dependencies — deliberately avoids ASP.NET Core / Kestrel. The built-in HTTP layer (HttpHarker) is a thin wrapper around System.Net.HttpListener, keeping the footprint minimal for embedding.

Packages

Most users need Duets.Jint, which pulls in Duets automatically:

dotnet add package Duets.Jint

Package	Targets	Description
Duets	netstandard2.1; net8.0	Core library: session, declarations, transpiler interface
Duets.Jint	netstandard2.1; net8.0	Jint backend; depends on Duets
Duets.Pad	netstandard2.1; net8.0	DuetsPad browser debug pad; depends on Duets and HttpHarker
HttpHarker	netstandard2.1; net8.0	Lightweight HTTP server (also available standalone)

Pre-release builds are available on nuget.tksk.io.

To build from source, the repository requires the .NET 10 SDK or later.

Quick Start

Add Duets.Jint — no Node.js required:

using var session = await DuetsSession.CreateAsync();
Console.WriteLine(session.Evaluate("Math.sqrt(2)")); // 1.4142135623730951

To call .NET types from TypeScript, enable CLR interop:

using var session = await DuetsSession.CreateAsync(config => config
    .UseJint(opts => opts.AllowClr()));

session.Execute("typings.usingNamespace('System.IO')");

Console.WriteLine(session.Evaluate("""
    const files: string[] = Directory.GetFiles('.');
    files.map(f => Path.GetFileName(f)).join(', ')
    """));

To serve the DuetsPad browser debug pad (package Duets.Pad) with Monaco editor, live .NET type completions, Canvas, and Timeline:

using var server = new HttpServer("http://127.0.0.1:17375/");
using var pad = server.UseContentTypeDetection().UseDuetsPad(configure: opts =>
    opts.SessionFactory = () => DuetsSession.CreateAsync(c => c.UseJint(o => o.AllowClr())));
await server.RunAsync(); // open http://127.0.0.1:17375/

More examples in samples/.

Project Structure

• src/
  • Duets/ — Core library: session, declarations, transpiler interface
  • Duets.Pad/ — DuetsPad browser debug pad (Editor / Canvas / Timeline / Immediate)
  • Duets.Jint/ — Jint backend: JintScriptEngine, BabelTranspiler, TypeScriptService, ExtensionMethodRegistry
  • HttpHarker/ — Lightweight HttpListener-based HTTP server with middleware pipeline
  • Duets.Sandbox/ — Multi-mode debugging CLI (run with --help or batch → {"op":"help"} for usage)
• samples/ — Runnable file-based app examples, grouped per package
• docs/ — Architecture overview and design decision records
• tests/
  • Duets.Tests/ — Unit tests
  • Duets.Pad.Tests/ — Unit tests for Duets.Pad
  • HttpHarker.Tests/ — Unit tests for HttpHarker

DuetsPad

A browser debug pad served over HTTP: Monaco editor with live .NET type completions, output canvas, execution timeline, and a ui.* builder surface for interactive controls. See src/Duets.Pad/README.md for surfaces, keybindings, and the ui.* API.

HttpHarker

A minimal HTTP server library built on System.Net.HttpListener with a middleware pipeline. See src/HttpHarker/README.md for details.