wasmtime

TLDR

Run a WebAssembly file

$ wasmtime [program.wasm]

Run with directory access

$ wasmtime --dir [/path/to/dir] [program.wasm]

Invoke a specific function

$ wasmtime run --invoke '[add(1, 2)]' [program.wasm]

Run a WASI HTTP server

$ wasmtime serve [component.wasm]

Compile to native ahead-of-time

$ wasmtime compile [program.wasm] -o [program.cwasm]

Run compiled module

$ wasmtime run [program.cwasm]

Enable WASI features

$ wasmtime -S inherit-env [program.wasm]

SYNOPSIS

wasmtime [options] [command] [wasm-file] [args...]

wasmtime is a standalone WebAssembly runtime from the Bytecode Alliance. It executes WebAssembly modules and components outside the browser, supporting WASI (WebAssembly System Interface) for system access.
The runtime can execute both binary (.wasm) and text (.wat) WebAssembly files. For performance-critical applications, modules can be ahead-of-time compiled to native code using the compile subcommand.
By default, Wasmtime sandboxes modules with no access to system resources. Access to files, environment, and network must be explicitly granted through command-line options.
The serve subcommand runs WebAssembly components implementing the wasi:http/proxy interface as HTTP servers.

PARAMETERS

--dir path

Grant access to host directory.

--env key=value

Set environment variable.

--invoke expr

Invoke specific exported function.

-O, --optimize options

Optimization settings.

-C, --codegen options

Code generation settings.

-D, --debug options

Debug settings.

-W, --wasm options

WebAssembly semantics settings.

-S, --wasi options

WASI configuration (inherit-env, inherit-network).

--config file

Load settings from TOML file.

-h, --help

Display help.

-V, --version

Display version.

COMMANDS

run: Execute WebAssembly module (default).
serve: Run component as WASI HTTP server.
compile: AOT compile to native code.
config: Manage Wasmtime configuration.
wast: Execute WebAssembly spec tests.

CAVEATS

WASI is not fully POSIX-compatible. Some system calls may not be available. Ahead-of-time compiled modules are platform-specific. Component Model support is evolving.

HISTORY

Wasmtime was developed by the Bytecode Alliance, a nonprofit organization including Mozilla, Fastly, Intel, and Red Hat. It serves as a reference implementation for WebAssembly outside the browser and drives development of WASI and the Component Model standards.