wasmtime

<strong>A standalone runtime for
<a href="https://webassembly.org/">WebAssembly</a></strong>

A Bytecode Alliance project

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Installation

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

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

This script installs into $WASMTIME_HOME (defaults to $HOME/.wasmtime), and executable is placed in $WASMTIME_HOME/bin.

After running the install script above, follow the on-screen instructions.

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

For additional installation options, refer to the online book CLI installation page.

Documentation on Wasmtime's currently supported versions can be found in the online book documentation.

Example

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

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

and compile it into a WebAssembly component with:

rustup target add wasm32-wasip2
rustc hello.rs --target wasm32-wasip2

Once compiled, you can run your component:

wasmtime hello.wasm

You should see the following output:

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.)

Features

• 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:

• Rust - the [wasmtime crate]
• C - the wasm.h, wasi.h, and wasmtime.h headers, CMake
• C++ - the wasmtime.hh header
• Python - the [wasmtime PyPI package]
• .NET - the [Wasmtime NuGet package]
• Go - the [wasmtime-go repository]
• Ruby - the [wasmtime gem]

Languages supported by the community:

• Elixir - the [wasmex hex package]
• Perl - the [Wasm Perl package's Wasm::Wasmtime]

Documentation

📚 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.