12 releases (6 breaking)

✓ Uses Rust 2018 edition

0.8.0 Oct 2, 2019
0.7.0 Sep 12, 2019
0.6.0 Aug 1, 2019
0.5.7 Jul 23, 2019
0.2.1 Feb 28, 2019
Download history 16/week @ 2019-06-15 17/week @ 2019-06-22 12/week @ 2019-06-29 45/week @ 2019-07-06 18/week @ 2019-07-13 17/week @ 2019-07-20 26/week @ 2019-07-27 53/week @ 2019-08-03 20/week @ 2019-08-10 10/week @ 2019-08-24 33/week @ 2019-08-31 39/week @ 2019-09-07 34/week @ 2019-09-14 128/week @ 2019-09-21

147 downloads per month

MIT license

15K SLoC

Wasmer logo

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Wasmer is a standalone WebAssembly runtime for running WebAssembly outside of the browser, supporting WASI and Emscripten.

Install the Wasmer CLI with:

curl https://get.wasmer.io -sSfL | sh

Note: Wasmer is also available on Windows


Wasmer runtime can be used as a library embedded in different languages, so you can use WebAssembly anywhere:

  Language Author(s) Maintenance Release Stars
Rust logo Rust Wasmer actively developed last release number of Github stars
C logo C/C++ Wasmer actively developed last release number of Github stars
Python logo Python Wasmer actively developed last release number of Github stars
Go logo Go Wasmer actively developed last release number of Github stars
PHP logo PHP Wasmer actively developed last release number of Github stars
Ruby logo Ruby Wasmer actively developed last release number of Github stars
Postgres logo Postgres Wasmer actively developed last release number of Github stars
C# logo C#/.Net Miguel de Icaza actively developed last release number of Github stars
R logo R Dirk Schumacher actively developed number of Github stars
Swift logo Swift Mark Malström passively maintained number of Github stars
your language is missing?


Wasmer can execute both the standard binary format (.wasm) and the text format defined by the WebAssembly reference interpreter (.wat).

Once installed, you will be able to run any WebAssembly files (including Lua, PHP, SQLite and nginx!):

# Run Lua
wasmer run examples/lua.wasm

You can find more wasm/wat examples in the examples directory.

With wapm

Installing Wasmer through wasmer.io includes wapm, the WebAssembly Package Manager.

wapm allows you to easily download, run, and distribute WebAssembly binaries.

# Install cowsay globally
wapm install -g cowsay

# Run cowsay
wapm run cowsay "Hello, world!"

For more information about wapm, check out the website and this example program.

Code Structure

Wasmer is structured into different directories:

  • src: code related to the Wasmer executable itself
  • lib: modularized libraries that Wasmer uses under the hood
  • examples: some useful examples for getting started with Wasmer


Building Wasmer requires rustup.

To build Wasmer on Windows, download and run rustup-init.exe then follow the onscreen instructions.

To build on other systems, run:

curl https://sh.rustup.rs -sSf | sh

Other dependencies

Please select your operating system:



If you have Homebrew installed:

brew install cmake

Or, if you have MacPorts:

sudo port install cmake

Debian-based Linuxes

Debian-based Linuxes

sudo apt install cmake pkg-config libssl-dev



pkg install cmake


Windows (MSVC)

Windows support is experimental. WASI is fully supported, but Emscripten support is in the works (this means nginx and Lua do not work on Windows - you can track the progress on this issue).

  1. Install Visual Studio

  2. Install Rust for Windows

  3. Install Python for Windows. The Windows x86-64 MSI installer is fine. Make sure to enable "Add python.exe to Path" during installation.

  4. Install Git for Windows. Allow it to add git.exe to your PATH (default settings for the installer are fine).

  5. Install CMake. Ensure CMake is in your PATH.

  6. Install LLVM 8.0


Rustc Version 1.37+

Wasmer is built with Cargo, the Rust package manager.

The Singlepass backend requires nightly, so if you want to use it,

Set Rust Nightly:

rustup default nightly

Otherwise an up to date (see badge above) version of stable Rust will work.

And install Wasmer

# checkout code
git clone https://github.com/wasmerio/wasmer.git
cd wasmer

# install tools
make release-clif # To build with cranelift (default)

make release-llvm # To build with llvm support

make release-singlepass # To build with singlepass support

# or
make release # To build with singlepass, cranelift and llvm support


Thanks to spec tests we can ensure 100% compatibility with the WebAssembly spec test suite.

You can run all the tests with:

rustup default nightly
make test

Testing backends

Each backend can be tested separately:

  • Singlepass: make singlepass
  • Cranelift: make cranelift
  • LLVM: make llvm

Testing integrations

Each integration can be tested separately:

  • Spec tests: make spectests
  • Emscripten: make emtests
  • WASI: make wasi
  • Middleware: make middleware
  • C API: make capi


Benchmarks can be run with:

make bench-[backend]

# for example
make bench-singlepass


Wasmer is an open project guided by strong principles, aiming to be modular, flexible and fast. It is open to the community to help set its direction.

Below are some of the goals of this project (in order of priority):

  • It should be 100% compatible with the WebAssembly spec tests
  • It should be fast (partially achieved)
  • Support WASI - released in 0.3.0
  • Support Emscripten calls (in the works)
  • Support Go JS ABI calls


If you would like to know how Wasmer works under the hood, please see docs/architecture.md.


Wasmer is primarily distributed under the terms of the MIT license (LICENSE).



~87K SLoC