vaern

An agent-native JavaScript & TypeScript runtime. Vaern runs TypeScript directly, with fetch and an HTTP server built in, on an embedded QuickJS-ng engine driven by Rust and Tokio. Capability sandboxing, tool-calling, MCP and replayable runs are being built into the engine itself.

VaernJS is a DevLogix project · licensed MIT

Status: v0.0.6, early native runtime

This release ships the native vaern binary for Linux, macOS and Windows. The API surface is small and will change before v1.0.

Works today

• vaern run <file>: JavaScript and TypeScript, with types stripped at load time and line numbers kept
• Relative ES module imports, and ES module packages already installed in node_modules
• console, setTimeout / setInterval, queueMicrotask
• process.argv, process.env, process.exit()
• fetch with Headers, Response, AbortController, redirects and timeouts (hyper and rustls)
• URL, URLSearchParams, TextEncoder and TextDecoder
• serve() from vaern:http, an HTTP server with Web-standard Request / Response and streamed bodies
• readFile, writeFile and appendFile from vaern:fs
• Uncaught exceptions, unhandled rejections and throwing timers exit non-zero with a file:line:col location

Not implemented yet

• node:* modules, CommonJS packages and downloading packages
• Capability sandboxing (vaern.toml)
• agent(), tool(), MCP, budgets and vaern replay

TypeScript enum, namespace and decorators are rejected with a located error, because they emit runtime code that type stripping cannot produce.

Install

npm install -g @vaernjs/vaern      # global CLI
npx @vaernjs/vaern --version       # without installing

npm installs one prebuilt binary for your platform through optionalDependencies, the same way esbuild does. Nothing is downloaded in a postinstall script; the platform packages are ordinary npm packages gated by os and cpu.

| Platform | Package | |---|---| | Linux x86_64 | @vaernjs/vaern-linux-x64 | | Linux arm64 | @vaernjs/vaern-linux-arm64 | | macOS arm64 | @vaernjs/vaern-darwin-arm64 | | macOS x86_64 | @vaernjs/vaern-darwin-x64 | | Windows x86_64 | @vaernjs/vaern-win32-x64 |

Linux binaries need glibc 2.35 or newer. On an unsupported platform, or when optional dependencies are skipped, vaern falls back to a small diagnostics CLI. Run vaern doctor there to see why.

Quick start

// latest.ts
interface Manifest {
  name: string;
  version: string;
}

const res = await fetch("https://registry.npmjs.org/@vaernjs/vaern/latest");
const pkg = (await res.json()) as Manifest;
console.log(`${pkg.name} ${pkg.version}, HTTP ${res.status}`);

vaern run latest.ts

Programmatic use

const { binaryPath, hasNativeBinary, vaern } = require("@vaernjs/vaern");

if (hasNativeBinary()) vaern(["run", "app.ts"]);

Links

• Website: vaernjs.tech
• DevLogix: devlogix.com.pk
• Repository: github.com/vaernjs/vaern
• Issues: github.com/vaernjs/vaern/issues
• npm: @vaernjs/vaern

Licence

MIT License. Copyright (c) 2026 DEVLOGIX TECHNOLOGY (PRIVATE) LIMITED (DevLogix). See LICENSE.

Development

git clone https://github.com/vaernjs/vaern.git && cd vaern
cargo build --release
npm run check          # pre-publish validation
npm run pack:dry       # inspect exactly what would be published

Issues and pull requests welcome. We would rather be corrected now than wrong later.