Wasmtime is a standalone runtime for WebAssembly, WASI, and the Component Model by the Bytecode Alliance.

WebAssembly (abbreviated Wasm) is a binary instruction format that is designed to be a portable compilation target for programming languages. Wasm binaries typically have a .wasm file extension. In this documentation, we'll also use the textual representation of the binary files, which have a .wat file extension.

WASI (the WebAssembly System Interface) defines interfaces that provide a secure and portable way to access several operating-system-like features such as filesystems, networking, clocks, and random numbers.

The Component Model is a Wasm architecture that provides a binary format for portable, cross-language composition. More specifically, it supports the use of interfaces via which components can communicate with each other. WASI is defined in terms of component model interfaces.

Wasmtime 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. It strives to be

  • Fast: Wasmtime is built on the optimizing Cranelift code generator.
  • Secure: Wasmtime's development is strongly focused on correctness and security.
  • Configurable: Wasmtime uses sensible defaults, but can also be configured to provide more fine-grained control over things like CPU and memory consumption.
  • Standards Compliant: Wasmtime passes the official WebAssembly test suite and the Wasmtime developers are intimately engaged with the WebAssembly standards process.

This documentation is intended to serve a number of purposes and within you'll find:

... and more! The source for this guide lives on GitHub and contributions are welcome!