HTML & static sites

Bun’s bundler has first-class support for HTML. Build static sites, landing pages, and web applications with zero configuration. Just point Bun at your HTML file and it handles everything else.

index.html

<!doctype html>
<html>
  <head>
    <link rel="stylesheet" href="./styles.css" />
    <script src="./app.ts" type="module"></script>
  </head>
  <body>
    <img src="./logo.png" />
  </body>
</html>

To get started, pass HTML files to bun.

terminal

bun ./index.html

Bun v1.3.3
ready in 6.62ms
→ http://localhost:3000/
Press h + Enter to show shortcuts

Bun’s development server provides powerful features with zero configuration:

Automatic Bundling - Bundles and serves your HTML, JavaScript, and CSS
Multi-Entry Support - Handles multiple HTML entry points and glob entry points
Modern JavaScript - TypeScript & JSX support out of the box
Smart Configuration - Reads tsconfig.json for paths, JSX options, experimental decorators, and more
Plugins - Plugins for TailwindCSS and more
ESM & CommonJS - Use ESM and CommonJS in your JavaScript, TypeScript, and JSX files
CSS Bundling & Minification - Bundles CSS from <link> tags and @import statements
Asset Management - Automatic copying & hashing of images and assets; Rewrites asset paths in JavaScript, CSS, and HTML

Single Page Apps (SPA)

When you pass a single .html file to Bun, Bun will use it as a fallback route for all paths. This makes it perfect for single page apps that use client-side routing:

terminal

bun index.html

Bun v1.3.3
ready in 6.62ms
→ http://localhost:3000/
Press h + Enter to show shortcuts

Your React or other SPA will work out of the box — no configuration needed. All routes like /about, /users/123, etc. will serve the same HTML file, letting your client-side router handle the navigation.

index.html

<!doctype html>
<html>
  <head>
    <title>My SPA</title>
    <script src="./app.tsx" type="module"></script>
  </head>
  <body>
    <div id="root"></div>
  </body>
</html>

Multi-page apps (MPA)

Some projects have several separate routes or HTML files as entry points. To support multiple entry points, pass them all to bun:

terminal

bun ./index.html ./about.html

Bun v1.3.3
ready in 6.62ms
→ http://localhost:3000/
Routes:
  / ./index.html
  /about ./about.html
Press h + Enter to show shortcuts

This will serve:

index.html at /
about.html at /about

Glob patterns

To specify multiple files, you can use glob patterns that end in .html:

terminal

bun ./**/*.html

Bun v1.3.3
ready in 6.62ms
→ http://localhost:3000/
Routes:
  / ./index.html
  /about ./about.html
Press h + Enter to show shortcuts

Path normalization

The base path is chosen from the longest common prefix among all the files.

terminal

bun ./index.html ./about/index.html ./about/foo/index.html

Bun v1.3.3
ready in 6.62ms
→ http://localhost:3000/
Routes:
  / ./index.html
  /about ./about/index.html
  /about/foo ./about/foo/index.html
Press h + Enter to show shortcuts

JavaScript, TypeScript, and JSX

Bun’s transpiler natively implements JavaScript, TypeScript, and JSX support. Learn more about loaders in Bun.

Bun’s transpiler is also used at runtime.

ES Modules & CommonJS

You can use ESM and CJS in your JavaScript, TypeScript, and JSX files. Bun will handle the transpilation and bundling automatically. There is no pre-build or separate optimization step. It’s all done at the same time. Learn more about module resolution in Bun.

CSS

Bun’s CSS parser is also natively implemented (clocking in around 70,000 lines of Rust). It’s also a CSS bundler. You can use @import in your CSS files to import other CSS files. For example:

@import "./abc.css";

.container {
  background-color: blue;
}

body {
  background-color: red;
}

This outputs:

styles.css

body {
  background-color: red;
}

.container {
  background-color: blue;
}

Referencing local assets in CSS

You can reference local assets in your CSS files.

styles.css

body {
  background-image: url("./logo.png");
}

This will copy ./logo.png to the output directory and rewrite the path in the CSS file to include a content hash.

styles.css

body {
  background-image: url("./logo-[ABC123].png");
}

Importing CSS in JavaScript

To associate a CSS file with a JavaScript file, you can import it in your JavaScript file.

app.ts

import "./styles.css";
import "./more-styles.css";

This generates ./app.css and ./app.js in the output directory. All CSS files imported from JavaScript will be bundled into a single CSS file per entry point. If you import the same CSS file from multiple JavaScript files, it will only be included once in the output CSS file.

Plugins

The dev server supports plugins.

Tailwind CSS

To use TailwindCSS, install the bun-plugin-tailwind plugin:

terminal

# Or any npm client
bun install --dev bun-plugin-tailwind

Then, add the plugin to your bunfig.toml:

bunfig.toml

[serve.static]
plugins = ["bun-plugin-tailwind"]

Then, reference TailwindCSS in your HTML via <link> tag, @import in CSS, or import in JavaScript.

index.html
styles.css
app.ts

index.html

<!-- Reference TailwindCSS in your HTML -->
<link rel="stylesheet" href="tailwindcss" />

styles.css

@import "tailwindcss";

app.ts

import "tailwindcss";

Only one of those are necessary, not all three.

Inline environment variables

Bun can replace process.env.* references in your JavaScript and TypeScript with their actual values at build time. This is useful for injecting configuration like API URLs or feature flags into your frontend code.

Dev server (runtime)

To inline environment variables when using bun ./index.html, configure the env option in your bunfig.toml:

bunfig.toml

[serve.static]
env = "PUBLIC_*"  # only inline env vars starting with PUBLIC_ (recommended)
# env = "inline"  # inline all environment variables
# env = "disable" # disable env var replacement (default)

This only works with literal process.env.FOO references, not import.meta.env or indirect access like const env = process.env; env.FOO.If an environment variable is not set, you may see runtime errors like ReferenceError: process is not defined in the browser.

Then run the dev server:

terminal

PUBLIC_API_URL=https://api.example.com bun ./index.html

Build for production

When building static HTML for production, use the env option to inline environment variables:

terminal

# Inline all environment variables
bun build ./index.html --outdir=dist --env=inline

# Only inline env vars with a specific prefix (recommended)
bun build ./index.html --outdir=dist --env=PUBLIC_*

build.ts

// Inline all environment variables
await Bun.build({
  entrypoints: ["./index.html"],
  outdir: "./dist",
  env: "inline", 
});

// Only inline env vars with a specific prefix (recommended)
await Bun.build({
  entrypoints: ["./index.html"],
  outdir: "./dist",
  env: "PUBLIC_*", 
});

Example

Given this source file:

app.ts

const apiUrl = process.env.PUBLIC_API_URL;
console.log(`API URL: ${apiUrl}`);

And running with PUBLIC_API_URL=https://api.example.com:

terminal

PUBLIC_API_URL=https://api.example.com bun build ./index.html --outdir=dist --env=PUBLIC_*

The bundled output will contain:

dist/app.js

const apiUrl = "https://api.example.com";
console.log(`API URL: ${apiUrl}`);

Echo console logs from browser to terminal

Bun’s dev server supports streaming console logs from the browser to the terminal. To enable, pass the --console CLI flag.

terminal

bun ./index.html --console

Bun v1.3.3
ready in 6.62ms
→ http://localhost:3000/
Press h + Enter to show shortcuts

Each call to console.log or console.error will be broadcast to the terminal that started the server. This is useful to see errors from the browser in the same place you run your server. This is also useful for AI agents that watch terminal output. Internally, this reuses the existing WebSocket connection from hot module reloading to send the logs.

Edit files in the browser

Bun’s frontend dev server has support for Automatic Workspace Folders in Chrome DevTools, which lets you save edits to files in the browser.

Keyboard Shortcuts

While the server is running:

o + Enter - Open in browser
c + Enter - Clear console
q + Enter (or Ctrl+C) - Quit server

Build for Production

When you’re ready to deploy, use bun build to create optimized production bundles:

terminal

bun build ./index.html --minify --outdir=dist

build.ts

await Bun.build({
  entrypoints: ["./index.html"],
  outdir: "./dist",
  minify: true,
});

Currently, plugins are only supported through Bun.build’s API or through bunfig.toml with the frontend dev server

not yet supported in bun build’s CLI.

Watch Mode

You can run bun build --watch to watch for changes and rebuild automatically. This works nicely for library development.

You’ve never seen a watch mode this fast.

Plugin API

Need more control? Configure the bundler through the JavaScript API and use Bun’s builtin HTMLRewriter to preprocess HTML.

build.ts

await Bun.build({
  entrypoints: ["./index.html"],
  outdir: "./dist",
  minify: true,

  plugins: [
    {
      // A plugin that makes every HTML tag lowercase
      name: "lowercase-html-plugin",
      setup({ onLoad }) {
        const rewriter = new HTMLRewriter().on("*", {
          element(element) {
            element.tagName = element.tagName.toLowerCase();
          },
          text(element) {
            element.replace(element.text.toLowerCase());
          },
        });

        onLoad({ filter: /\.html$/ }, async args => {
          const html = await Bun.file(args.path).text();

          return {
            // Bun's bundler will scan the HTML for <script> tags, <link rel="stylesheet"> tags, and other assets
            // and bundle them automatically
            contents: rewriter.transform(html),
            loader: "html",
          };
        });
      },
    },
  ],
});

What Gets Processed?

Bun automatically handles all common web assets:

Scripts (<script src>) are run through Bun’s JavaScript/TypeScript/JSX bundler
Stylesheets (<link rel="stylesheet">) are run through Bun’s CSS parser & bundler
Images (<img>, <picture>) are copied and hashed
Media (<video>, <audio>, <source>) are copied and hashed
Any <link> tag with an href attribute pointing to a local file is rewritten to the new path, and hashed

All paths are resolved relative to your HTML file, so you can organize your project however you want.

This is a work in progress

Need more plugins
Need more configuration options for things like asset handling
Need a way to configure CORS, headers, etc.

How this works

This is a small wrapper around Bun’s support for HTML imports in JavaScript.

Standalone HTML

You can bundle your entire frontend into a single self-contained .html file with no external dependencies using --compile --target=browser. All JavaScript, CSS, and images are inlined directly into the HTML.

terminal

bun build --compile --target=browser ./index.html --outdir=dist

Learn more in the Standalone HTML docs.

Adding a backend to your frontend

To add a backend to your frontend, you can use the “routes” option in Bun.serve. Learn more in the full-stack docs.

Core

Development Server

Asset Processing

Single File Executable

Extensions

Optimization

Migration

HTML & static sites

Single Page Apps (SPA)

Multi-page apps (MPA)

Glob patterns

Path normalization

JavaScript, TypeScript, and JSX

ES Modules & CommonJS

CSS

Referencing local assets in CSS

Importing CSS in JavaScript

Plugins

Tailwind CSS

Inline environment variables

Dev server (runtime)

Build for production

Example

Echo console logs from browser to terminal

Edit files in the browser

Keyboard Shortcuts

Build for Production

Watch Mode

Plugin API

What Gets Processed?

How this works

Standalone HTML

Adding a backend to your frontend

​Single Page Apps (SPA)

​Multi-page apps (MPA)

​Glob patterns

​Path normalization

​JavaScript, TypeScript, and JSX

​ES Modules & CommonJS

​CSS

​Referencing local assets in CSS

​Importing CSS in JavaScript

​Plugins

​Tailwind CSS

​Inline environment variables

​Dev server (runtime)

​Build for production

​Example

​Echo console logs from browser to terminal

​Edit files in the browser

​Keyboard Shortcuts

​Build for Production

​Watch Mode

​Plugin API

​What Gets Processed?

​How this works

​Standalone HTML

​Adding a backend to your frontend

Single Page Apps (SPA)

Multi-page apps (MPA)

Glob patterns

Path normalization

JavaScript, TypeScript, and JSX

ES Modules & CommonJS

CSS

Referencing local assets in CSS

Importing CSS in JavaScript

Plugins

Tailwind CSS

Inline environment variables

Dev server (runtime)

Build for production

Example

Echo console logs from browser to terminal

Edit files in the browser

Keyboard Shortcuts

Build for Production

Watch Mode

Plugin API

What Gets Processed?

How this works

Standalone HTML

Adding a backend to your frontend