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.NET embedding of Wasmtime

A Bytecode Alliance project

CI status Latest Version Documentation


You can add a package reference with the .NET SDK:

$ dotnet add package --version 0.39.1-preview2 wasmtime

Note that the --version option is required because the package is currently prerelease.


For this introduction, we'll be using a simple WebAssembly module that imports a hello function and exports a run function:

  (func $hello (import "" "hello"))
  (func (export "run") (call $hello))

To use this module from .NET, create a new console project:

$ mkdir wasmintro
$ cd wasmintro
$ dotnet new console

Next, add a reference to the Wasmtime package:

$ dotnet add package --version 0.39.1-preview2 wasmtime

Replace the contents of Program.cs with the following code:

using System;
using Wasmtime;

namespace WasmIntro
    class Program
        static void Main(string[] args)
            using var engine = new Engine();

            using var module = Module.FromText(
                "(module (func $hello (import \"\" \"hello\")) (func (export \"run\") (call $hello)))"

            using var linker = new Linker(engine);
            using var store = new Store(engine);

                Function.FromCallback(store, () => Console.WriteLine("Hello from C#!"))

            var instance = linker.Instantiate(store, module);
            var run = instance.GetAction(store, "run");

An Engine is created and then a WebAssembly module is loaded from a string in WebAssembly text format.

A Linker defines a function called hello that simply prints a hello message.

The module is instantiated and the instance's run export is invoked.

To run the application, simply use dotnet:

$ dotnet run

This should print Hello from C#!.



Use dotnet to build the repository:

$ dotnet build Wasmtime.sln

This will download the latest development snapshot of Wasmtime for your platform.


Use dotnet to run the unit tests:

$ dotnet test Wasmtime.sln

Creating the NuGet package

Use dotnet to create a NuGet package:

$ cd src
$ dotnet pack Wasmtime.sln -c Release /p:Packing=true

This will create a .nupkg file in src/bin/Release.

By default, local builds will use a -dev suffix for the package to differentiate between official packages and development packages.