17 unstable releases (5 breaking)

0.5.5 Nov 29, 2023
0.5.2 Sep 21, 2023
0.4.0 May 19, 2023
0.3.0 Mar 15, 2023
0.1.0 Nov 30, 2022

#354 in WebAssembly

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563 downloads per month


2.5K SLoC


Extism is a lightweight framework for building with WebAssembly (Wasm). It supports running Wasm code on servers, the edge, CLIs, IoT, browsers and everything in between. Extism is designed to be "universal" in that it supports a common interface, no matter where it runs.

Note: One of the primary use cases for Extism is building extensible software & plugins. You want to be able to execute arbitrary, untrusted code from your users? Extism makes this safe and practical to do.

Additionally, Extism adds some extra utilities on top of standard Wasm runtimes. For example, we support persistent memory/module-scope variables, secure & host-controlled HTTP without WASI, runtime limiters & timers, simpler host function linking, and more. Extism users build:

  • plug-in systems
  • FaaS platforms
  • code generators
  • web applications
  • & much more...

Run WebAssembly In Your App

Pick a SDK to import into your program, and refer to the documentation to get started:

Type Language Source Code Package
Rust SDK Rust SDK https://github.com/extism/extism/tree/main/runtime Crates.io
JS SDK JS SDK https://github.com/extism/js-sdk
(supports Web, Node, Deno & Bun!)
Elixir SDK Elixir SDK https://github.com/extism/elixir-sdk Hex
Go SDK Go SDK https://github.com/extism/go-sdk Go mod
Haskell SDK Haskell SDK https://github.com/extism/haskell-sdk Hackage
Java SDK Java SDK https://github.com/extism/java-sdk Sonatype
.NET SDK .NET SDK https://github.com/extism/dotnet-sdk
(supports C# & F#!)
OCaml SDK OCaml SDK https://github.com/extism/ocaml-sdk opam
PHP SDK PHP SDK https://github.com/extism/php-sdk Packagist
Python SDK Python SDK https://github.com/extism/python-sdk PyPi
Ruby SDK Ruby SDK https://github.com/extism/ruby-sdk RubyGems
Zig SDK Zig SDK https://github.com/extism/zig-sdk N/A
C SDK C SDK https://github.com/extism/extism/tree/main/libextism N/A
C++ SDK C++ SDK https://github.com/extism/cpp-sdk N/A

Compile WebAssembly to run in Extism Hosts

Extism Hosts (running the SDK) must execute WebAssembly code that has a PDK library compiled in to the .wasm binary. PDKs make it easy for plug-in / extension code authors to read input from the host and return data back, read provided configuration, set/get variables, make outbound HTTP calls if allowed, and more.

Pick a PDK to import into your Wasm program, and refer to the documentation to get started:

Type Language Source Code Package
Rust PDK Rust PDK https://github.com/extism/rust-pdk Crates.io
JS PDK JS PDK https://github.com/extism/js-pdk N/A
Go PDK Go PDK https://github.com/extism/go-pdk Go mod
Haskell PDK Haskell PDK https://github.com/extism/haskell-pdk Hackage
AssemblyScript PDK AssemblyScript PDK https://github.com/extism/assemblyscript-pdk NPM
.NET PDK .NET PDK https://github.com/extism/dotnet-pdk
(supports C# & F#!)
C PDK C PDK https://github.com/extism/c-pdk N/A
Zig PDK Zig PDK https://github.com/extism/zig-pdk N/A



If you experience any problems or have any questions, please join our Discord and let us know. Our community is very responsive and happy to help get you started.


Head to the project website for more information and docs. Also, consider reading an overview of Extism and its goals & approach.


Thank you for considering a contribution to Extism, we are happy to help you make a PR or find something to work on!

The easiest way to start would be to join the Discord or open an issue on the extism/proposals issue tracker, which can eventually become an Extism Improvement Proposal (EIP).

For more information, please read the Contributing guide.

Who's behind this?

Extism is an open-source product from the team at:

Reach out and tell us what you're building! We'd love to help: hello@dylibso.com


~536K SLoC