Quickstart

Build your first app with Bun

Overview#

Build a minimal HTTP server with Bun.serve, run it locally, then evolve it by installing a package.

Prerequisites: Bun installed and available on your PATH. See installation for setup.

Step 1

Initialize a new project with bun init.

terminal
bun init my-app

bun init prompts you to pick a template: Blank, React, or Library. For this guide, pick Blank.

terminal
bun init my-app
✓ Select a project template: Blank

+ .gitignore
+ CLAUDE.md
+ .cursor/rules/use-bun-instead-of-node-vite-npm-pnpm.mdc -> CLAUDE.md
+ index.ts
+ tsconfig.json (for editor autocomplete)
+ README.md

The new my-app directory contains a basic Bun app.

Step 2

Run index.ts with bun run.

terminal
cd my-app
bun run index.ts
Hello via Bun!

Step 3

Replace the contents of index.ts with the following code:

index.ts
const server = Bun.serve({
  port: 3000,
  routes: {
    "/": () => new Response('Bun!'),
  }
});

console.log(`Listening on ${server.url}`);

Run index.ts again.

terminal
bun run index.ts
Listening on http://localhost:3000/

Visit http://localhost:3000 to test the server. You should see a page that says "Bun!".

Seeing TypeScript errors on Bun?

bun init installs Bun's TypeScript declarations and configures your tsconfig.json. If you're trying out Bun in an existing project, you may see a type error on the Bun global.

To fix this, first install @types/bun as a dev dependency.

terminal
bun add -d @types/bun

Then add the following to your compilerOptions in tsconfig.json:

tsconfig.json
{
  "compilerOptions": {
    "lib": ["ESNext"],
    "target": "ESNext",
    "module": "Preserve",
    "moduleDetection": "force",
    "moduleResolution": "bundler",
    "allowImportingTsExtensions": true,
    "verbatimModuleSyntax": true,
    "noEmit": true
  }
}

Step 4

Install the figlet package and its type declarations. Figlet is a utility for converting strings into ASCII art.

terminal
bun add figlet
bun add -d @types/figlet # TypeScript users only

Update index.ts to use figlet in routes.

index.ts
import figlet from 'figlet'; 

const server = Bun.serve({
  port: 3000,
  routes: {
    "/": () => new Response('Bun!'),
    "/figlet": () => { 
      const body = figlet.textSync('Bun!'); 
      return new Response(body); 
    } 
  }
});

console.log(`Listening on ${server.url}`);

Run index.ts again.

terminal
bun run index.ts
Listening on http://localhost:3000/

Visit http://localhost:3000/figlet to test the server. You should see a page that says "Bun!" in ASCII art.

____              _
| __ ) _   _ _ __ | |
|  _ \| | | | '_ \| |
| |_) | |_| | | | |_|
|____/ \__,_|_| |_(_)

Step 5

Now add some HTML. Create a new file called index.html:

index.html
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Bun</title>
  </head>
  <body>
    <h1>Bun!</h1>
  </body>
</html>

Then, import this file in index.ts and serve it from the root / route.

index.ts
import figlet from 'figlet';
import index from './index.html'; 

const server = Bun.serve({
  port: 3000,
  routes: {
    "/": index, 
    "/figlet": () => {
      const body = figlet.textSync('Bun!');
      return new Response(body);
    }
  }
});

console.log(`Listening on ${server.url}`);

Run index.ts again.

terminal
bun run index.ts
Listening on http://localhost:3000/

Visit http://localhost:3000 to test the server. You should see the static HTML page.

You've built an HTTP server with Bun and installed a package.

Run a script#

Bun can also execute "scripts" from your package.json. Add the following script:

package.json
{
  "name": "my-app",
  "module": "index.ts",
  "type": "module",
  "private": true,
  "scripts": { 
    "start": "bun run index.ts" 
  }, 
  "devDependencies": {
    "@types/bun": "latest"
  },
  "peerDependencies": {
    "typescript": "^6"
  }
}

Then run it with bun run start.

terminal
bun run start
Listening on http://localhost:3000/
⚡️ Performance — bun run is roughly 28x faster than npm run (6ms vs 170ms of overhead).