Wasmtime is a standalone wasm-only runtime for WebAssembly, using the Cranelift JIT.

It runs WebAssembly code outside of the Web, and can be used both as a command-line utility or as a library embedded in a larger application.

Wasmtime passes the WebAssembly spec testsuite, and supports a new system API proposal called WebAssembly System Interface, or WASI.

Wasmtime includes a git submodule; in order to build it, it's necessary to obtain a full checkout, like this:

git clone --recurse-submodules https://github.com/CraneStation/wasmtime.git

To build an optimized version of Wasmtime, use Cargo:

cargo build --release

There are Rust, C, and C++ toolchains that can compile programs with WASI. See the WASI intro for more information, and the WASI tutorial for a tutorial on compiling and running programs using WASI and wasmtime, as well as an overview of the filesystem sandboxing system.

Wasmtime does not yet implement Spectre mitigations, however this is a subject of ongoing research.

Additional goals for Wasmtime include:

• Support a variety of host APIs (not just WASI Core), with fast calling sequences, and develop proposals for additional API modules to be part of WASI. Reference Sysroot.
• Implement the proposed WebAssembly C API.
• Facilitate testing, experimentation, and development around the Cranelift and Lightbeam JITs.
• Develop a native ABI used for compiling WebAssembly suitable for use in both JIT and AOT to native object files.

Wasmtime exposes an API for JIT compilation through the wasmtime-jit subcrate, which depends on wasmtime-environ and wasmtime-runtime for the ABI and runtime support respectively. However, this API is not documented and subject to change. Please use at your own risk!

Build the individual crates as such:

cargo build --package wasmtime-jit

Wasmtime does not currently publish these crates on crates.io. They may be included as a git dependency, like this:

[dependencies]
wasmtime-environ = { git = "https://github.com/CraneStation/wasmtime", rev = "somecommithash" }
wasmtime-runtime = { git = "https://github.com/CraneStation/wasmtime", rev = "somecommithash" }
wasmtime-jit = { git = "https://github.com/CraneStation/wasmtime", rev = "somecommithash" }

All three crates must be specified as dependencies for wasmtime-jit to build correctly, at the moment.

It's Wasmtime.