8 breaking releases

0.27.0 May 21, 2021
0.26.0 Apr 5, 2021
0.25.0 Mar 16, 2021
0.21.0 Nov 5, 2020
0.19.0 Jul 16, 2020

#171 in WebAssembly

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291 downloads per month

Apache-2.0 WITH LLVM-exception

13K SLoC


A standalone runtime for WebAssembly

A Bytecode Alliance project

build status zulip chat supported rustc stable Documentation Status

Guide | Contributing | Website | Chat


The Wasmtime CLI can be installed on Linux and macOS with a small install script:

curl https://wasmtime.dev/install.sh -sSf | bash

Windows or otherwise interested users can download installers and binaries directly from the GitHub Releases page.


If you've got the Rust compiler installed then you can take some Rust source code:

fn main() {
    println!("Hello, world!");

and compile/run it with:

$ rustup target add wasm32-wasi
$ rustc hello.rs --target wasm32-wasi
$ wasmtime hello.wasm
Hello, world!


  • Fast. Wasmtime is built on the optimizing Cranelift code generator to quickly generate high-quality machine code either at runtime or ahead-of-time. Wasmtime's runtime is also optimized for cases such as efficient instantiation, low-overhead transitions between the embedder and wasm, and scalability of concurrent instances.

  • Secure. Wasmtime's development is strongly focused on the correctness of its implementation with 24/7 fuzzing donated by Google's OSS Fuzz, leveraging Rust's API and runtime safety guarantees, careful design of features and APIs through an RFC process, a security policy in place for when things go wrong, and a release policy for patching older versions as well. We follow best practices for defense-in-depth and known protections and mitigations for issues like Spectre. Finally, we're working to push the state-of-the-art by collaborating with academic researchers to formally verify critical parts of Wasmtime and Cranelift.

  • Configurable. Wastime supports a rich set of APIs and build time configuration to provide many options such as further means of restricting WebAssembly beyond its basic guarantees such as its CPU and Memory consumption. Wasmtime also runs in tiny environments all the way up to massive servers with many concurrent instances.

  • WASI. Wasmtime supports a rich set of APIs for interacting with the host environment through the WASI standard.

  • Standards Compliant. Wasmtime passes the official WebAssembly test suite, implements the official C API of wasm, and implements future proposals to WebAssembly as well. Wasmtime developers are intimately engaged with the WebAssembly standards process all along the way too.

Language Support

You can use Wasmtime from a variety of different languages through embeddings of the implementation:


📚 Read the Wasmtime guide here! 📚

The wasmtime guide is the best starting point to learn about what Wasmtime can do for you or help answer your questions about Wasmtime. If you're curious in contributing to Wasmtime, it can also help you do that!

It's Wasmtime.


~394K SLoC