created_at2023-12-09 14:11:06.473154
updated_at2024-05-15 11:58:16.203055
descriptionA tiny WebAssembly interpreter
Henry Gressmann (explodingcamera)




A tiny WebAssembly Runtime written in safe Rust

docs.rs Crates.io Crates.io

Why TinyWasm?

  • Tiny: TinyWasm is designed to be as small as possible without significantly compromising performance or functionality (< 4000 LLOC).
  • Portable: TinyWasm runs on any platform that Rust can target, including no_std, with minimal external dependencies.
  • Safe: No unsafe code is used in the runtime (rkyv which uses unsafe code can be used for serialization, but it is optional).


As of version 0.3.0, TinyWasm successfully passes all the WebAssembly 1.0 tests in the WebAssembly Test Suite. Work on the 2.0 tests is ongoing. This enables TinyWasm to run most WebAssembly programs, including executing TinyWasm itself compiled to WebAssembly (see examples/wasm-rust.rs). The results of the testsuites are available here.

The API is still unstable and may change at any time, so you probably don't want to use it in production yet. TinyWasm isn't primarily designed for high performance; it focuses more on simplicity, size, and portability. More details on its performance can be found in BENCHMARKS.md.

Future Development: The first major version will focus on improving the API and adding support for WASI. While doing so, I also want to further simplify and reduce the codebase's size and improve the parser's performance.

Supported Proposals

Proposal Implementation Status Version
Mutable Globals Fully implemented 0.2.0
Multi-value Fully implemented 0.2.0
Sign-extension operators Fully implemented 0.2.0
Bulk Memory Operations Fully implemented 0.4.0
Reference Types Partially implemented N/A
Multiple Memories Partially implemented N/A
Memory64 Partially implemented N/A


TinyWasm can be used through the tinywasm-cli CLI tool or as a library in your Rust project. Documentation can be found here.


$ cargo add tinywasm


The CLI is mainly available for testing purposes, but can also be used to run WebAssembly programs.

$ cargo install tinywasm-cli
$ tinywasm-cli --help

Feature Flags

  • std
    Enables the use of std and std::io for parsing from files and streams. This is enabled by default.
  • logging
    Enables logging using the log crate. This is enabled by default.
  • parser
    Enables the tinywasm-parser crate. This is enabled by default.
  • archive
    Enables pre-parsing of archives. This is enabled by default.

With all these features disabled, TinyWasm only depends on core, alloc ,and libm and can be used in no_std environments. Since libm is not as performant as the compiler's math intrinsics, it is recommended to use the std feature if possible (at least for now), especially on wasm32 targets.


Big thanks to the authors of the following projects, which have inspired and influenced TinyWasm:

  • wasmi - an efficient and lightweight WebAssembly interpreter that also runs on no_std environments
  • wasm3 - a high performance WebAssembly interpreter written in C
  • wazero - a zero-dependency WebAssembly interpreter written in go
  • wain - a zero-dependency WebAssembly interpreter written in Rust

I encourage you to check these projects out if you're looking for a more mature and feature-complete WebAssembly interpreter.


Licensed under either of Apache License, Version 2.0 or MIT license at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in TinyWasm by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

Note: The GitHub repository contains a Submodule (crates/tinywasm-parser/data) which is licensed only under the Apache License, Version 2.0. This data is generated from the WebAssembly Specification and is only used for testing purposes and not included in the final binary.

Commit count: 263

cargo fmt