bytecodealliance

bytecodealliance/wasmtime

A lightweight WebAssembly runtime that is fast, secure, and standards-compliant

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README.md

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<div align="center">
  <h1><code>wasmtime</code></h1>

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

<strong>A <a href="https://bytecodealliance.org/">Bytecode Alliance</a> project</strong>

<h3>
    <a href="https://bytecodealliance.github.io/wasmtime/">Guide</a>
    <span> | </span>
    <a href="https://bytecodealliance.github.io/wasmtime/contributing.html">Contributing</a>
    <span> | </span>
    <a href="https://wasmtime.dev/">Website</a>
    <span> | </span>
    <a href="https://bytecodealliance.zulipchat.com/#narrow/stream/217126-wasmtime">Chat</a>
  </h3>
</div>

## Installation

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

```console
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](https://github.com/bytecodealliance/wasmtime/releases) page.

For additional installation options, refer to the [online book CLI installation page](https://docs.wasmtime.dev/cli-install.html).

Documentation on Wasmtime's currently supported versions can be found [in the
online book
documentation](https://docs.wasmtime.dev/stability-release.html#current-versions).

## Example

If you've got the [Rust compiler
installed](https://www.rust-lang.org/tools/install) then you can take some Rust
source code:

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

and compile it into a WebAssembly component with:

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

Once compiled, you can run your component:

```console
wasmtime hello.wasm
```

You should see the following output:

```text
Hello, world!
```

(Note: make sure you installed Rust using the [`rustup`][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.)

[rustup]: https://rustup.rs

## 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][release policy], 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](https://wasi.dev).

* **[Standards Compliant]**. Wasmtime passes the [official WebAssembly test
  suite](https://github.com/WebAssembly/testsuite), implements the [official C
  API of wasm](https://github.com/WebAssembly/wasm-c-api), and implements
  [future proposals to WebAssembly](https://github.com/WebAssembly/proposals) as
  well. Wasmtime developers are intimately engaged with the WebAssembly
  standards process all along the way too.

[Wasmtime]: https://github.com/bytecodealliance/wasmtime
[Cranelift]: https://cranelift.dev/
[Google's OSS Fuzz]: https://google.github.io/oss-fuzz/
[security policy]: https://bytecodealliance.org/security
[RFC process]: https://github.com/bytecodealliance/rfcs
[release policy]: https://docs.wasmtime.dev/stability-release.html
[Secure]: https://docs.wasmtime.dev/security.html
[Configurable]: https://docs.rs/wasmtime/latest/wasmtime/struct.Config.html
[WASI]: https://docs.rs/wasmtime-wasi/latest/wasmtime_wasi/
[Standards Compliant]: https://docs.wasmtime.dev/stability-tiers.html

## 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][c-headers], [CMake](crates/c-api/CMakeLists.txt)
* **C++** - the [`wasmtime.hh` header][c-headers]
* **[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`]

[Rust]: https://bytecodealliance.github.io/wasmtime/lang-rust.html
[C]: https://bytecodealliance.github.io/wasmtime/lang-c.html
[`wasmtime` crate]: https://crates.io/crates/wasmtime
[c-headers]: https://bytecodealliance.github.io/wasmtime/c-api/
[Python]: https://bytecodealliance.github.io/wasmtime/lang-python.html
[`wasmtime` PyPI package]: https://pypi.org/project/wasmtime/
[.NET]: https://bytecodealliance.github.io/wasmtime/lang-dotnet.html
[`Wasmtime` NuGet package]: https://www.nuget.org/packages/Wasmtime
[Go]: https://bytecodealliance.github.io/wasmtime/lang-go.html
[`wasmtime-go` repository]: https://pkg.go.dev/github.com/bytecodealliance/wasmtime-go
[Ruby]: https://bytecodealliance.github.io/wasmtime/lang-ruby.html
[`wasmtime` gem]: https://rubygems.org/gems/wasmtime
[Elixir]: https://docs.wasmtime.dev/lang-elixir.html
[`wasmex` hex package]: https://hex.pm/packages/wasmex
[`Wasm` Perl package's `Wasm::Wasmtime`]: https://metacpan.org/pod/Wasm::Wasmtime

## Documentation

[📚 Read the Wasmtime guide here! 📚][guide]

The [wasmtime guide][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][contributing]!

[contributing]: https://bytecodealliance.github.io/wasmtime/contributing.html
[guide]: https://bytecodealliance.github.io/wasmtime

---

It's Wasmtime.

Repository info

Default branch: main
Latest version: v50.0.1
Created: 29/08/2017
Last activity: 04/11/2026
License: Apache-2.0
Open issues: 880
Watchers: 164

Topics

aot cranelift jit lightweight portable runtime rust sandbox standalone wasi wasm wasmtime webassembly

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