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The tiny all-in-one development tool for modern web apps, in a single 2mb file with no dependencies.

All the features you'd expect and more, from development to production:

πŸ”¨ Β  No entry points or pages to configure - just HTML files with <script type=module>
🦦   Safely import "packages" from npm without installation
πŸ“¦ Β  Smart bundling and caching for npm dependencies
↻ Β  Hot reloading for modules, Preact components and CSS
⚑️   Lightning-fast JSX support that you can debug in the browser
πŸ’„ Β  Import CSS files and CSS Modules (*.module.css)
πŸ”© Β  Out-of-the-box support for TypeScript
πŸ“‚ Β  Static file serving with hot reloading of CSS and images
πŸ—œ Β  Highly optimized Rollup-based production output (wmr build)
πŸ“‘ Β  Crawls and pre-renders your app's pages to static HTML at build time
🏎   Built-in HTTP2 in dev and prod (wmr serve --http2)
πŸ”§ Β  Supports Rollup plugins, even in development where Rollup isn't used

Quickstart (recommended)

Create a new project in seconds using create-wmr:

npm init wmr your-project-name


yarn create wmr your-project-name

πŸ’ If you'd like ESLint to be set up for you, add --eslint to the command. Note: this will use 150mb of disk space.

Manual installation and setup

While it's best to use the quickstart method above, WMR caters to folks who want to start from scratch too.

There isn't really anything WMR-specific to set up - the steps here are essentially the what you would do to use a simple HTTP server.

1. First, install wmr using npm or yarn:

npm i -D wmr
# or:
yarn add -D wmr

πŸ”₯ You can also use npx wmr anywhere!

2. Next you'll want to create a public/index.html file. You can use this example, though there's really nothing special about this HTML file. Just make sure your scripts are ES Modules by including type="module":

<!DOCTYPE html>
		<link rel="stylesheet" href="/style.css" />
		<script type="module" src="/index.js"></script>

πŸ’ Why public/? Keeping your code and assets in public/ prevents files like node_modules and package.json from being accessed by browsers. It also helps separate your web-facing code from other things like build scripts and output files. WMR auto-detects your public/ directory, or you can specify your own by passing --public src to any of the commands.

3. To test things out, create that index.js file and add a simple Preact component to it:

import { render } from 'preact';

function App() {
	return <h1>Hello World!</h1>;

render(<App />, document.body);

4. Now we can add some scripts to our package.json. There's one for starting the dev server, another to create a production build. A third script serves that production build for easy local testing:

	"scripts": {
		"start": "wmr",
		"build": "wmr build",
		"serve": "wmr serve --http2"

preact/compat is our compatibility layer that allows you to leverage the many libraries of the React ecosystem and use them with Preact. If this is something you'd like to use with WMR you can add an alias section as well to your package.json:

	"alias": {
		"react": "preact/compat",
		"react-dom": "preact/compat"

5. You're all set! As an extra step, if you'd like WMR to prerender your application to static HTML during production builds, replace render() with preact-iso:

-import { render } from 'preact';
+import hydrate from 'preact-iso/hydrate';

function App() {
  return <h1>Hello World!</h1>;

-render(<App />, document.body);
+hydrate(<App />);

+export async function prerender(data) {
+  // we use dynamic import to prevent this from being loaded in the browser:
+  return (await import('preact-iso/prerender')).default(<App {} />);

Configuration and plugins

WMR supports a wmr.config.js (or wmr.config.mjs) configuration file, which can be used to set WMR's options and inject Rollup plugins or Polka/Express middleware.

You can export a default config function applied to all WMR commands, or individual functions for start, build and serve:

// wmr.config.mjs
import someRollupPlugin from '@rollup/plugin-xyz';

/** @param {import('wmr').Options} config */
export default async function (config) {
	if (config.mode === 'build') {
			// add any Rollup plugins:

	if (config.mode === 'serve') {
			// add any Polka middleware:
			function myPolkaMiddleware(req, res, next) {
				res.setHeader('X-Foo', 'bar');

// Or configure each WMR command separately:
export async function start(config) {
	// equivalent to `config.mode === 'start'`
export async function build(config) {
	// equivalent to `config.mode === 'build'`
export async function serve(config) {
	// equivalent to `config.mode === 'serve'`

Note: remember to add "type":"module" to your package.json or use the .mjs file extension to make the file a JS module.

See the full list of options.


Most applications can be built with WMR without any configuration or plugins. However, sometimes a bit of configuration can help optimize the output or simplify your development workflow.

WMR supports Rollup plugins, and there's a growing list of configurations and recipes in the wiki, including:


git clone
cd wmr
npm i

# run the demo (no compile)
npm run demo

# build and serve the demo for prod
npm run demo:prod && npm run demo:serve

# build the single-file CLI:
npm run build
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