Overview

Bun is a JavaScript runtime environment designed to offer an integrated and performance-focused solution for web development. Introduced in 2022, Bun consolidates the functionalities of a runtime, a package manager, a bundler, and a test runner into a single executable, aiming to streamline the development workflow and reduce setup complexity Bun Runtime Overview. It is built using the Zig programming language and leverages Apple's JavaScriptCore engine, which contributes to its reported startup times and execution speeds Bun's JavaScript Engine.

The primary use cases for Bun include server-side JavaScript applications, where its speed can benefit API backends and microservices. For frontend development, Bun functions as a bundler, capable of processing TypeScript and JSX natively, and as a package manager that can install dependencies at a rapid pace Bun Bundler documentation. Additionally, its design makes it suitable for general-purpose scripting and automation tasks, offering a fast environment for executing JavaScript and TypeScript files directly.

Bun targets developers seeking performance improvements and a simplified toolchain. Its compatibility with a significant portion of the Node.js API allows for the migration of existing Node.js projects with minimal modifications, reducing the barrier to adoption Bun's Node.js API compatibility. This compatibility extends to support for npm packages, enabling developers to use their existing dependency ecosystem. While it shares goals with other modern runtimes like Deno, Bun differentiates itself by offering an all-in-one approach that includes built-in development tools, rather than relying on external utilities for bundling or package management.

The project emphasizes web standards and aims to provide a consistent environment across different development stages, from local development to production deployment. Its focus on reducing latency and improving throughput positions it as an option for applications where execution speed is a critical factor. The architecture of Bun is designed to minimize overhead and optimize resource utilization, making it a consideration for resource-constrained environments or applications requiring high concurrency.

Key features

  • Bun Runtime: A JavaScript and TypeScript runtime built on JavaScriptCore, offering fast startup and execution speeds for server-side and client-side code Bun Runtime documentation.
  • Bun Bundler: An integrated JavaScript and TypeScript bundler that supports common web formats like ES Modules and CommonJS, with built-in optimizations for production deployments Bun Bundler documentation.
  • Bun Package Manager: A fast npm-compatible package manager that supports existing package.json files and installs dependencies rapidly Bun Package Manager guide.
  • Bun Test Runner: A built-in test runner compatible with Jest-like APIs, providing a fast environment for unit and integration testing Bun Test Runner documentation.
  • Node.js API Compatibility: Provides support for a subset of Node.js APIs, enabling developers to run existing Node.js applications and use npm packages without extensive refactoring Bun's Node.js API compatibility.
  • Web API Support: Implements standard Web APIs such as fetch, WebSocket, and ReadableStream, aligning with modern web development practices Bun Global APIs.
  • TypeScript and JSX Support: Native support for TypeScript and JSX, eliminating the need for separate transpilation steps during development Bun TypeScript support.
  • Hot Reloading: Includes capabilities for hot reloading, allowing developers to see code changes reflected instantly without restarting the application Bun Hot Reloading.

Pricing

Bun is an entirely free and open-source project. There are no licensing fees, subscription costs, or tiered plans for its use. The source code is publicly available, allowing for community contributions and modifications Bun homepage.

Feature Availability Notes
Bun Runtime Free Full access to the JavaScript runtime.
Bun Bundler Free Full access to the JavaScript and TypeScript bundler.
Bun Package Manager Free Full access to the npm-compatible package manager.
Bun Test Runner Free Full access to the integrated test runner.
Community Support Free Support available via community channels and documentation.

Pricing as of 2026-06-26

Common integrations

  • Node.js Ecosystem: Bun is largely compatible with existing Node.js modules and APIs, allowing it to integrate with a wide range of npm packages and tools designed for Node.js environments Bun's Node.js API compatibility.
  • Web Frameworks: Can be used with popular web frameworks like React, Vue, and Svelte for frontend development, and frameworks such as Express, Hono, or Elysia for backend services React documentation on starting new projects.
  • Databases: Integrates with database drivers and ORMs that support Node.js, including those for PostgreSQL, MySQL, and MongoDB Sequelize ORM getting started guide.
  • Development Tools: Works with code editors like VS Code, which offers extensions for JavaScript and TypeScript development, and version control systems like Git.
  • Cloud Platforms: Deployable on various cloud platforms and serverless environments that support custom runtimes or Node.js applications, such as AWS Lambda, Google Cloud Functions, and Vercel.

Alternatives

  • Node.js: An open-source, cross-platform JavaScript runtime environment that executes JavaScript code outside a web browser, widely used for server-side applications and tooling.
  • Deno: A secure JavaScript, TypeScript, and WebAssembly runtime with built-in tooling, developed by the creators of Node.js.
  • Vite: A next-generation frontend tooling solution that provides a fast development server and a build tool, often used in conjunction with other runtimes.
  • Next.js: A React framework for building full-stack web applications, offering server-side rendering, static site generation, and API routes Next.js documentation.
  • Remix: A full-stack web framework that focuses on web standards and provides nested routing, server-side rendering, and a robust data story Remix quickstart guide.

Getting started

To begin using Bun, you can install it via a shell script. Once installed, you can execute JavaScript or TypeScript files directly, run a development server, or manage packages.

First, install Bun:

curl -fsSL https://bun.sh/install | bash

After installation, you can verify it by checking the Bun version:

bun --version

Now, create a simple TypeScript file named hello.ts:

// hello.ts

function greet(name: string): string {
  return `Hello, ${name}! Welcome to Bun.`;
}

const userName = "fwdgrade";
console.log(greet(userName));

// You can also use Bun's built-in HTTP server for a simple web application
// import { serve } from "bun";

// serve({
//   fetch(request) {
//     const url = new URL(request.url);
//     if (url.pathname === "/") {
//       return new Response("Hello from Bun!", { status: 200 });
//     }
//     return new Response("404 Not Found", { status: 404 });
//   },
//   port: 3000,
// });
// console.log("Bun server listening on http://localhost:3000");

Execute the TypeScript file directly using Bun:

bun run hello.ts

This command will output: Hello, fwdgrade! Welcome to Bun.

You can also initialize a new project and install dependencies using Bun's package manager:

mkdir my-bun-app
cd my-bun-app
bun init -y
bun add express

This sequence creates a new project directory, initializes a package.json, and then installs the express package using Bun's package manager, demonstrating its integrated capabilities.