Mozilla Rhino is a JavaScript interpreter written in Java.

Rhino is an open source JavaScript engine. It is developed entirely in Java and managed by the Mozilla Foundation. The Foundation also provides another implementation of JavaScript engine written in C named SpiderMonkey.

Rhino converts JavaScript scripts into classes. Rhino works in both compiled as well as interpreted mode. It is intended to be used in server-side applications, hence there is no built-in support for the Web browser objects that are commonly associated with JavaScript.

Rhino can be used as a debugger by making use of the Rhino shell. It can be used in applications by embedding Rhino.