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NetWasm is an independent project that compiles C#-generated CIL to WebAssembly, with its own CoreLib and runtime. Its creator, Zion Sati, describes it as a way to build WASI Preview 2 components that include the runtime pieces an application uses—not as a Microsoft project or a replacement announced by Microsoft. A small program can be a good trial, but compatibility depends on NetWasm’s supported APIs and your host environment.
What NetWasm does
In Sati’s description, the flow begins with Roslyn compiling C# into CIL. NetWasm then follows reachable code and compiles that CIL toward WebAssembly, supplying a separate CoreLib and runtime. It links the pieces required by the application rather than shipping a conventional full .NET runtime alongside it. Sati says the resulting application does not require CoreCLR, Mono, dotnet.js, or managed application DLLs beside the component. These are the author’s descriptions of the design, not an independent audit.
The aim is to start with a small runtime and an explicit supported surface, rather than trim a runtime designed for a different environment. Sati describes some functionality as opt-in or pay-for-use: time-zone data can be opted into, and source-generated JSON is available as a pay-for-use option. The project also describes selected ports for LINQ, HTTP JSON, configuration, options, dependency injection, and caching, plus TUnit support through dotnet test. A package name or familiar API is not, by itself, proof that a particular NuGet workload is compatible.
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What the 88,419-byte example means
Sati reports an uncompressed output size of 88,419 bytes for a clean Release build of Console.WriteLine(42);. He says that figure includes the program, required CoreLib and runtime pieces, and a precise Boehm garbage collector. It is a measurement for that specific small program, not a size guarantee for other C# applications.
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The source does not provide a controlled size or performance comparison against other .NET-to-WebAssembly approaches. To assess fit, compare the same workload and build conditions, and inspect what each output includes. The reported hello-world size cannot establish that NetWasm is generally smaller or faster.
WASI and the component target
NetWasm’s stated main target is a WASI Preview 2 component. WASI provides the host interface through which a WebAssembly component receives capabilities from its environment. The official WASI project describes version 0.2 as a modular collection of APIs defined with WIT and the WebAssembly Component Model. Its documentation describes version 0.3 as building on 0.2 with native asynchronous primitives, including future and stream types. That context does not establish NetWasm support for Preview 3.
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The Rust documentation for wasm32-wasip2 explains Preview 2’s reliance on the Component Model and characterizes it as an “island of stability” while noting that WASI remains under active development. The practical implication is that a component still depends on a compatible host and the capabilities it grants; building for WASI does not automatically provide unrestricted access to a machine’s files or network.
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Sati describes NetWasm as early and says it has known bugs. At the time of his September 23, 2026 article, he listed these unsupported areas:
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- Expression trees.
- Managed threading.
- General managed
File,FileStream, andDirectoryAPIs. - Raw sockets.
Runtime reflection and dynamic are design non-goals, and the author says NetWasm does not provide a runtime type-name catalog. These boundaries matter for code that discovers types or members at runtime, depends on reflection-heavy frameworks, or expects the usual managed filesystem, networking, or threading APIs.
A C# program compiling successfully does not establish that an entire application, its dependencies, or a workload written in another .NET language will work. Check the current project support inventory against the APIs and packages your application actually uses before choosing it for a larger workload.
Try a small C# program
Sati describes an SDK-based command-line workflow. With the .NET SDK installed, the sequence is:
- Install the templates:
dotnet new install NetWasm.Templates. - Create an app:
dotnet new netwasm-app. - Restore dependencies:
dotnet restore. - Run it:
dotnet run. - Publish a Release build:
dotnet publish -c Release.
The author says a published component can be run directly with Wasmtime if that runtime is installed. He also offers a browser playground, where compilation is described as running locally in the browser. As project commands, templates, and support can change, consult the current README and project inventory before relying on these instructions.
Best Value
How to decide whether NetWasm fits
NetWasm is worth investigating when a small C# workload needs a WASI component and its dependencies fit the project’s supported surface. Before committing, check:
Quick Recap
- APIs and packages: Confirm the specific framework APIs and dependency versions your program needs are supported.
- Runtime behavior: Identify reflection,
dynamic, expression trees, or managed threading in your code and dependencies. - Environment access: Determine whether the workload requires managed filesystem APIs or raw sockets, which Sati lists as unsupported.
- Host compatibility: Match the generated component’s WASI target to the runtime and capabilities available in deployment.
- Output and build process: Build your own reproducible workload and examine the artifact; do not extrapolate from the single reported console-program size.
- License terms: Sati’s article says the compiler and tooling are source available under the NetWasm Community License, while CoreLib, runtime, templates, and ported libraries are MIT licensed. Review the current repository license files for the components you plan to use or distribute.
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