Amber runs JavaScript and TypeScript files from a single amber binary. It ships a test runner, a bundler, a single-file compiler, a small package installer, an HTTP serve command, and a permission sandbox for running agent tools.

Amber is open source under the MIT license. The source lives at github.com/zh30/amberjs.

What Amber is

A V8 runtime written in Rust. The CLI runs scripts on V8 through src/runtime_minimal.rs. TypeScript and TSX are transpiled with oxc before they run.
One binary, many commands. amber run, amber test, amber bundle, amber compile, amber install, and amber serve all live in the same executable.
A Node.js and Web API surface with written contracts. Each Stable API has a contract file in docs/ and an integration test in tests/. The contract lists what works and where it stops.
A host for agent tools. amber run --sandbox denies file, network, environment, and process access unless you allow it. amber session and amber mcp call exported functions from a tool file over JSON-RPC.

What Amber is not

Amber is not a drop-in replacement for Node.js, Bun, or Deno. Many Node modules are partial, and several are Preview. Use the compatibility page to check an API before you depend on it.

Amber does not publish performance numbers today. Older benchmark tables in the repository are historical and were not re-run for this release.

How to read this manual

Every capability carries one of four labels:

Label	Meaning
Stable	Pinned by a contract document and an executable test that runs in CI. Limits are listed next to the API.
Preview	In the default build and usable, but the contract or edge cases are still being tightened.
Experimental	Code exists, but it is not a product promise until it is re-verified.
Not supported	Deliberately out of scope. Amber fails closed instead of pretending.

The single source of truth for these labels is docs/CURRENT_SCOPE.md. If this site and that file disagree, the file wins.

Introduction

What Amber is

What Amber is not

How to read this manual

Next steps