SpiderMonkey is Mozilla’s JavaScript and WebAssembly Engine, used in Firefox, Servo and various other projects. It is written in C++, Rust and JavaScript. You can embed it into C++ and Rust projects, and it can be run as a stand-alone shell. It can also be compiled to WASI; see our online demo.

What's New

Read more in the SpiderMonkey Blog

SpiderMonkey Internals

Understanding the engine

In-depth Articles:

Building and Contributing

Embedding SpiderMonkey

Where to find us

While we strongly recommend using Matrix chat if you have questions, we also maintain a non-exhaustive list of people who have volunteered their expertise on specific components of SpiderMonkey. For example, you might need to know who to needinfo about IonMonkey in Bugzilla…