Bun: A Fast, All-in-One Toolkit for JavaScript and TypeScript

Bun is more than a runtime. It is an all-in-one toolkit designed to simplify and accelerate JavaScript and TypeScript development. At its core lies a single, self-contained executable named bun, which bundles a blazing-fast runtime, a Node.js-compatible package manager, and a suite of built-in developer tools. Written in Zig and powered by JavaScriptCore, Bun aims to deliver dramatically faster startup times and lower memory usage compared to traditional Node.js workflows. This blog post explores what Bun is, how it works, and how you can start using it in your projects today.

Introduction to Bun and its ecosystem

• One executable, many tools: bun is not just a runtime. It includes a test runner, a script runner, and a Node.js-compatible package manager, all accessible from the same command line.
• Speed as a core principle: Bun’s design focuses on reducing startup times and memory overhead, enabling faster development cycles and quicker feedback loops.
• Built for modern JS and TS: Bun supports JavaScript and TypeScript out of the box, with JSX and other modern features ready to use.
• Drop-in Node replacement: Bun is described as a drop-in replacement for Node.js in many development scenarios, allowing teams to adopt Bun with minimal friction.

In this guide, you’ll discover how Bun fits into your development workflow, what you can do with its built-in tools, and how to get started quickly—whether you’re on Linux, macOS, Windows, or inside a container.

What is Bun? A closer look

• Bun as a runtime: At the heart of Bun is the Bun runtime, a fast JavaScript runtime designed to serve as a drop-in replacement for Node.js. It aims to boot projects faster and run with lower memory usage.
• Written in Zig, powered by JavaScriptCore: Bun’s core engine is implemented in Zig and leverages JavaScriptCore to execute code efficiently.
• All-in-one tooling: Bun’s CLI implements multiple utilities:
• bun: the primary entrypoint for running scripts, starting development servers, and managing projects.
• bun test: a built-in test runner with modern testing capabilities.
• bun run: a script runner that executes commands defined in package.json.
• bun install: a package manager that handles dependencies (a Bun-native alternative to npm/yarn/pnpm).
• bunx: a package runner that allows executing binaries from the local project or the registry.
• Minimal changes to existing projects: Bun’s built-in tooling is designed to work with existing Node.js projects with little to no changes required.

Core features you’ll likely use every day

• Fast startup and light memory footprint: Core performance advantages are highlighted by Bun’s design choices, which aim to accelerate development iterations.
• Out-of-the-box TypeScript and JSX support: TS and JSX are supported without separate configuration, streamlining the experience for modern frontend and full-stack projects.
• All-in-one CLI experience: You manage dependencies, run tests, and execute scripts from a single toolchain, reducing context switching.

How Bun works under the hood

• The Bun runtime: A fast JavaScript runtime built to be a practical replacement for Node.js, enabling quick startup and lower memory usage.
• Zig-based implementation: The runtime is implemented in Zig, a language known for safety and performance, which contributes to Bun’s efficiency.
• JavaScriptCore as the engine: Bun relies on JavaScriptCore to execute JavaScript, delivering effective performance characteristics that complement Bun’s tooling.

Key components and their roles

• Runtime: The low-level engine that executes your JavaScript/TypeScript code with speed and efficiency.
• Package manager: bun install resolves dependencies and installs them in a Bun-specific manner, aiming for fast installs.
• Test runner: bun test provides an integrated testing experience with sensible defaults and modern testing features.
• Script runner: bun run executes scripts defined in package.json, aligning with typical npm/yarn workflows.
• Bunx: A convenient command for executing binaries and scripts, enabling quick access to project-specific binaries.

Getting started: Quick start and usage

• Run TS/JS files directly:
• bun run index.tsx
• Bun supports TS and JSX out of the box, making it straightforward to prototype and iterate.
• Run tests:
• bun test
• Start a project’s entry script:
• bun run start
• Install dependencies:
• bun install
• Execute a package binary:
• bunx cowsay 'Hello, world!'

Installation: Where Bun runs and how to install

Bun supports major platforms and architectures:

• Linux: x64 and arm64
• macOS: x64 and Apple Silicon
• Windows: x64 and arm64

Important notes

• Linux kernel recommendations: Kernel version 5.6 or higher is strongly recommended, but Bun works with a minimum of 5.1.
• x64 CPU caveats: If you encounter “illegal instruction” or similar errors, check Bun’s CPU requirements and baseline builds.

Install options (choose your preferred path)

• With install script (recommended):
• curl -fsSL https://bun.com/install | bash
• Windows (PowerShell):
• powershell -c "irm bun.sh/install.ps1 | iex"
• npm (global install):
• npm install -g bun
• Homebrew (macOS/Linux):
• brew tap oven-sh/bun
• brew install bun
• Docker (containerized):
• docker pull oven/bun
• docker run --rm --init --ulimit memlock=-1:-1 oven/bun

Upgrading Bun and canary builds

• To upgrade to the latest released version:
• bun upgrade
• For the latest canary build (built on every main commit):
• bun upgrade --canary
• Canary builds live alongside stable releases and can be helpful for testing upcoming features.

Quick links and guided paths

• Intro, What is Bun?, Installation, Quickstart, TypeScript, and more
• Runtime, Module resolution, Loaders, and Node.js compatibility notes
• Bundler, Tests, and API references
• Ecosystem guides (React, Prisma, Discourse Bot examples, Docker, Next.js, Nuxt, SvelteKit, and many more)
• HTMLRewriter, HTTP APIs, file I/O, streams, SQLite, PostgreSQL, Redis, and many other runtime capabilities
• Community and contributing resources

Practical usage: Bun in real-world workflows

• A unified developer experience: With bun, you can install packages, run scripts, test code, and ship applications without juggling multiple tools.
• Faster iteration cycles: The speed-focused design helps you iterate faster during development, from dependency installation to test execution.
• TS-first mindset: Native support for TypeScript makes it easier to adopt modern TypeScript patterns without heavy configuration overhead.
• Rich runtime APIs: Bun exposes a broad set of runtime features—from HTTP servers to file system utilities and streaming capabilities—enabling developers to build sophisticated applications with fewer dependencies.

Guides and ecosystem highlights

Bun’s ecosystem is expansive, with guides covering deployment, ecosystems, HTML rewriting, HTTP servers, and many runtime utilities. Here are some representative areas you’ll encounter:

• Deployment guides: Deploy to Vercel, Railway, Render, AWS Lambda, DigitalOcean, Google Cloud Run, and more.
• Binary and data handling: Conversions between blob, string, DataView, ReadableStream, and related data transformations.
• Ecosystem integrations: React with JSX, Prisma, Prisma Postgres, Upstash Redis, Drizzle ORM, Nuxt, Qwik, Astro, Remix, Vite, Next.js, and others.
• HTMLRewriter: Extract links and social meta tags for SEO and content extraction tasks.
• HTTP and networking: Build HTTP servers, routes, TLS configuration, fetch usage, and WebSocket support.
• File system and IO: Read, write, and transform files, streams, and directories; including advanced features like archives and tar handling.
• Testing and tooling: Jest-to-Bun migration considerations, test runners, mocks, snapshots, and coverage tooling.
• Utilities and process: Process control, IPC, environment variables, and time-related utilities.

Contributing and licensing

• Bun’s contributors guide provides the recommended process to start contributing to the project.
• Licensing information is available in the Project > License documentation.

Images and visuals

• The Bun logo and community badges from the Input are included to visually anchor this post:
• Logo:
• Discord badge:
• GitHub stars badge:
• Speed badge:

Closing thoughts: why choose Bun?

Bun positions itself as a pragmatic choice for developers seeking speed, simplicity, and a cohesive toolchain. By combining a fast runtime with a capable package manager, test runner, script runner, and a convenient binary for executing commands, Bun aims to reduce the friction commonly associated with JavaScript/TypeScript development. For teams starting from scratch, Bun offers a compelling path to faster installs, quicker test cycles, and easier project bootstrapping. For seasoned Node.js users, Bun promises a smoother upgrade path with minimal changes required to existing projects, while unlocking potential performance gains across the development lifecycle.

If you’re curious about Bun, the quickest path forward is to explore the official docs, try the install script on Linux or macOS, and run a few commands from the Bun CLI to experience the speed and simplicity firsthand. The ecosystem of guides and integrations continues to grow, making Bun not just a runtime, but a complete, modern toolkit for building JavaScript and TypeScript applications.