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A standalone runtime for WebAssembly

A Bytecode Alliance project

build status zulip chat supported rustc stable Documentation Status


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

curl -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 --target wasm32-wasi
$ wasmtime hello.wasm
Hello, world!

(Note: make sure you installed Rust using the rustup method in the official instructions above, and do not have a copy of the Rust toolchain installed on your system in some other way as well (e.g. the system package manager). Otherwise, the rustup target add... command may not install the target for the correct copy of Rust.)


  • 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 is optimized for efficient instantiation, low-overhead calls between the embedder and wasm, and scalability of concurrent instances.

  • Secure. Wasmtime's development is strongly focused on correctness and security. Building on top of Rust's runtime safety guarantees, each Wasmtime feature goes through careful review and consideration via an RFC process. Once features are designed and implemented, they undergo 24/7 fuzzing donated by Google's OSS Fuzz. As features stabilize they become part of a release, and when things go wrong we have a well-defined security policy in place to quickly mitigate and patch any issues. We follow best practices for defense-in-depth and integrate 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. Wasmtime uses sensible defaults, but can also be configured to provide more fine-grained control over things like CPU and memory consumption. Whether you want to run Wasmtime in a tiny environment or on massive servers with many concurrent instances, we've got you covered.

  • 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.

Languages supported by the Bytecode Alliance:

Languages supported by the community:


📚 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.