# `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](https://gitea.privatedns.org/xavi/nanowasm-design/)
to the WebAssembly language. A NanoWasm-compatible program can be built from
a MVP WebAssembly program with [`nwc`](https://gitea.privatedns.org/xavi/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](COMPARE.md) 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`](examples/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`](examples/proc_exit.c) defines the code required to
support the following minimal C program built with
[`wasi-sdk`](https://github.com/WebAssembly/wasi-sdk):

```c
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](LICENSE).

[`wasm-micro-runtime`]: https://github.com/bytecodealliance/wasm-micro-runtime
[`wasm3`]: https://github.com/wasm3/wasm3
[`wac`]: https://github.com/kanaka/wac
[`toywasm`]: https://github.com/yamt/toywasm