1 stable release

1.17.2 Feb 14, 2024

#185 in Embedded development


36K SLoC

Rhai - Embedded Scripting for Rust

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Rhai logo

Rhai is an embedded scripting language and evaluation engine for Rust that gives a safe and easy way to add scripting to any application.

Targets and builds

  • All CPU and O/S targets supported by Rust, including:
    • WebAssembly (WASM)
    • no-std
  • Minimum Rust version 1.66.0

Standard features

Protected against attacks

  • Don't Panic guarantee - Any panic is a bug. Rhai subscribes to the motto that a library should never panic the host system, and is coded with this in mind.
  • Sand-boxed - the scripting engine, if declared immutable, cannot mutate the containing environment unless explicitly permitted.
  • Rugged - protected against malicious attacks (such as stack-overflow, over-sized data, and runaway scripts etc.) that may come from untrusted third-party user-land scripts.
  • Track script evaluation progress and manually terminate a script run.
  • Passes Miri.

For those who actually want their own language


The scripts subdirectory contains sample Rhai scripts.

Below is the standard Fibonacci example for scripting languages:

// This Rhai script calculates the n-th Fibonacci number using a
// really dumb algorithm to test the speed of the scripting engine.

const TARGET = 28;
const REPEAT = 5;
const ANSWER = 317_811;

fn fib(n) {
    if n < 2 {
    } else {
        fib(n-1) + fib(n-2)

print(`Running Fibonacci(${TARGET}) x ${REPEAT} times...`);
print("Ready... Go!");

let result;
let now = timestamp();

for n in 0..REPEAT {
    result = fib(TARGET);

print(`Finished. Run time = ${now.elapsed} seconds.`);

print(`Fibonacci number #${TARGET} = ${result}`);

if result != ANSWER {
    print(`The answer is WRONG! Should be ${ANSWER}!`);

Project Site



See The Rhai Book for details on the Rhai scripting engine and language.


An Online Playground is available with syntax-highlighting editor, powered by WebAssembly.

Scripts can be evaluated directly from the editor.


Licensed under either of the following, at your choice:

Unless explicitly stated otherwise, any contribution intentionally submitted for inclusion in this crate, as defined in the Apache-2.0 license, shall be dual-licensed as above, without any additional terms or conditions.


~108K SLoC