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What is Bun? The All-in-One Runtime for Faster JS in 2026

Bun is a modern JavaScript runtime (a program that executes JavaScript code outside of a web browser) that combines a fast engine, a package manager, and a test runner into a single tool. By replacing traditional tools like Node.js and npm, Bun can speed up your development workflow by up to 20x while reducing the number of different programs you need to install. Most beginners can set up a high-performance web server with Bun in under 60 seconds using its built-in APIs.

Why are developers switching to Bun in 2026?

Speed is the primary reason most developers choose Bun over older runtimes like Node.js. Bun is built using Zig (a low-level programming language known for performance) and the JavaScriptCore engine, which powers the Safari web browser. This combination allows Bun to start up almost instantly, making it ideal for modern serverless functions (small pieces of code that run only when needed) and edge computing.

Another major draw is the "all-in-one" philosophy that simplifies your workspace. In the past, you had to install separate tools for running code, managing packages, and testing; Bun handles all of these natively. This reduces "dependency hell" (a situation where different software packages require conflicting versions of other software) and keeps your project folders much cleaner.

We’ve found that the built-in support for TypeScript (a version of JavaScript with added type safety features) is a massive time-saver for new developers. You no longer need to set up complex "transpilers" (tools that convert TypeScript into regular JavaScript) like Babel or tsc. You can simply name your file with a .ts extension and run it directly with Bun, which handles the conversion behind the scenes automatically.

What are the core features included in the box?

Bun functions as a package manager, which is a tool that automates the process of installing, upgrading, and configuring software libraries. It is fully compatible with the npm ecosystem, meaning you can use any of the millions of packages available on the npm registry. However, Bun installs these packages significantly faster than traditional tools by using advanced file-copying techniques.

The runtime also includes a built-in test runner, which is software used to verify that your code works as expected. It supports modern testing patterns found in frameworks like Vitest or the older Jest, but executes them with much lower overhead. This means your feedback loop—the time between writing code and seeing if it works—is nearly instantaneous.

Bun 2.x and higher also provide native support for modern web standards like Fetch (a way to make network requests) and WebSockets (a way to maintain a constant connection between a client and server). It even supports React 19 and Next.js 15 out of the box. You don't have to worry about importing external libraries for basic web functionality because it is already baked into the core system.

What do you need before getting started?

Before you install Bun, you should ensure your computer meets a few basic requirements. Don't worry if you've never used a "terminal" (a text-based interface for giving commands to your computer) before; we will walk through the commands together.

Hardware and OS Requirements:

  • macOS: Apple Silicon (M1/M2/M3/M4) or Intel chips are both supported.
  • Linux: Most distributions work, including those running on Windows Subsystem for Linux (WSL).
  • Windows: Bun now has native support for Windows 10 and 11, so you don't necessarily need WSL anymore.
  • Permissions: You will need "Admin" or "Sudo" rights to install the software globally on your machine.

How do you install Bun on your machine?

Follow these steps to get Bun running on your computer. The installation process is designed to be quick and non-intrusive.

Step 1: Open your terminal On Windows, search for "PowerShell" or "Command Prompt." On macOS, press Cmd + Space and type "Terminal."

Step 2: Run the installation command Copy and paste the following command into your terminal and press Enter:

# For macOS and Linux users
curl -fsSL https://bun.sh/install | bash

# For Windows users (using PowerShell)
powershell -c "irm bun.sh/install.ps1 | iex"

Step 3: Verify the installation Close your terminal and reopen it to ensure the new settings take effect. Type the following command to check your version:

bun --version

What you should see: You should see a version number like 2.0.4 or higher printed in the terminal. If you see this number, Bun is successfully installed and ready to use.

How do you manage packages with Bun?

Managing libraries (pre-written code you can use in your project) is one of Bun's strongest features. It uses a file called package.json to keep track of what your project needs to run.

Step 1: Initialize a project Create a new folder for your project, navigate into it in your terminal, and run:

bun init

Step 2: Install a library Let's install a popular library like "Lucide" (a collection of icons). Run the following command:

bun add lucide

Step 3: Check your files Look inside your folder to see what happened. You will notice a node_modules folder and a bun.lock file.

What you should see: The terminal will show a summary of how many packages were added and the exact time it took (usually under 100ms). The bun.lock file is a binary file that ensures everyone on your team installs the exact same versions of every library, making your project more stable.

How do you build your first web server?

Now that Bun is set up, let's create a simple web server. This server will listen for requests and send back a "Hello World" message.

Step 1: Create a file Create a new file in your project folder named server.ts.

Step 2: Add the server code Copy the following code into your server.ts file:

// Bun.serve starts a high-performance web server
const server = Bun.serve({
  port: 3000, // The server will run on this port
  fetch(request) {
    // This function runs every time someone visits your site
    return new Response("Welcome to Bun!");
  },
});

console.log(`Server is running at http://localhost:${server.port}`);

Step 3: Run the server Go back to your terminal and type:

bun server.ts

What you should see: The terminal will display "Server is running at http://localhost:3000". Open your web browser and visit that address; you will see the message "Welcome to Bun!" on the screen.

What are the common troubleshooting steps?

Even for experts, things sometimes go wrong during setup. It is normal to run into a few hurdles when learning a new tool for the first time.

  • "Command not found" error: This usually happens because your terminal doesn't know where Bun was installed. Try restarting your computer or manually adding the Bun folder to your "PATH" (a list of folders your computer searches for programs).
  • Permission Denied: If you get an error about permissions on Linux or macOS, you might need to use sudo before the command, though the standard Bun installer usually avoids this.
  • Version Mismatch: If a package isn't working, ensure you are using a modern version of Bun. You can update at any time by running bun upgrade.
  • Windows Execution Policy: On Windows, PowerShell might block the installation script. You can fix this by running Set-ExecutionPolicy RemoteSigned -Scope CurrentUser in your terminal before trying the install again.

Next Steps

Now that you have Bun installed and a basic server running, you are ready to explore more advanced topics. You might want to try connecting a database like SQLite (which Bun supports natively with a built-in driver) or building a full-stack application using Next.js 15.

The best way to learn is by doing. Try changing the text in your server.ts file or installing different packages from npm to see how they interact. Don't be afraid to break things; you can always delete the folder and start over in seconds.

For more technical details and API references, check out the official Bun documentation.

Read the Bun Documentation