`nanowasm`, the tiny Wasm interpreter that does not block you

This project is still unfinished and is not meant for production use.

This project aims to provide the most minimal Wasm interpreter possible in strictly portable ANSI C (C89/C90). It can run one or more Wasm applications concurrently, without threading. This project requires the Nanowasm extensions to the WebAssembly language. A NanoWasm-compatible program can be built from a MVP WebAssembly program with nwc.

Features

Portable ANSI C implementation. Runs on bare metal environments.
No dependencies other than an ANSI C (C89/C90) compiler.
Asynchronous interface that allows to run multiple applications concurrently, without threads.
I/O-agnostic implementation for maximum flexibility: read modules from a network, write the stack into a file, implement a MMU in software... Anything is possible!
Suitable for resource-constrained devices, such as microcontrollers.
No memory allocator required.
Supports both big-endian and little-endian architectures.

Comparison chart

Feature	`nanowasm`	[`wasm-micro-runtime`]	[`wasm3`]	[`wac`]	[`toywasm`]
Asynchronous interface	✅	❌	❌	❌	❌
I/O-agnostic	✅	❌	❌	❌	❌
No heap required	✅	❌	❌	❌	❌
Big-endian support	✅	⚠️	✅	❌	✅
No compiler-specific extensions	✅	❌	❌	❌	❌
C dialect	`c89`	`gnu99`	`c99`	`gnu99`	`c11`
Public functions	7	156	44	N/A	N/A
Minimal `.text` footprint	49 KiB	452 KiB	519 KiB	N/A	N/A
Per-module memory usage	~1016 bytes	N/A	N/A	N/A	N/A
Per-instance memory usage	~728 bytes	N/A	N/A	N/A	N/A

Also, see a detailed explanation behind the numbers above.

What `nanowasm` is not

As opposed to other interpreters, nanowasm prefers lower memory usage rather than run-time performance. Therefore, it should not be unfairly compared performance-wise against other interpreters.

How to build

Use the conventional process in CMake projects:

cmake -B <dir>
cmake --build <dir>

Examples

example/minimal.c provides the essential minimum code required to work with nanowasm i.e., without any imports. This is only meant as a starting point for implementations, and not as a standalone program.
example/proc_exit.c defines the code required to support the following minimal C program built with wasi-sdk:

int main()
{
    return 0;
}

License

nanowasm, a tiny WebAssembly/Wasm interpreter
Copyright (C) 2023-2025  Xavier Del Campo Romero

This Source Code Form is subject to the terms of the Mozilla Public
License, v. 2.0. If a copy of the MPL was not distributed with this
file, You can obtain one at https://mozilla.org/MPL/2.0/.

Also, see LICENSE.

nanowasm, the tiny Wasm interpreter that does not block you