Dev server

A simple web server for simple web developers. Does the minimal amount of work required for web development on modern web browsers. Specifically designed to work with the native es module loader available in all major browsers.

Resolves node-style module imports to browser-style

Browsers only accept fully resolved paths in module imports. This is infeasible when working with many dependencies in a project. This the only code transform this server does for you:

import { html } from 'lit-html';


import { html } from '../../node_modules/lit-html/lit-html.js';

This will become obsolete over time, as a similar behavior is being standardized in browsers. It's called import maps.

Note: import paths are only resolved within .js files. This means you cannot do a bare module import from your index.html:

      import { html } from 'lit-html'; // does not work

Please note that the owc-dev-server only resolves bare module specifiers, and does nothing to transform different module formats like CommonJS. If this is a requirement for you, please check out our rollup configuration.


npm i -D owc-dev-server


// package.json
"scripts": {
  "start": "owc-dev-server"

// bash
npm run start

// or via npx
npx owc-dev-server

Basic command

The most basic command that will work for most single page applications:

npx owc-dev-server --app-index index.html --open --watch

See the sections below for a detailed explanations of all command line options.

Static files

By default the server will just serve up static files from your current working directory:

npx owc-dev-server --open

You can open the server at a specific file/location:

npx owc-dev-server --open demo/my-file.html
npx owc-dev-server --open demo

To change the server's root directory:

npx owc-dev-server ./dist
# or
npx owc-dev-server --root-dir ./dist

Single Page App

For a SPA, you will want non-file requests to serve the app's index so that you can handle routing within your app. The browser will automatically open at your app's root path.

npx owc-dev-server --app-index index.html --open

Note: That this will require a <base href="/"> in your html head.

Component project

When working on a (web) component project, you will usually have a demo folder for local development:

npx owc-dev-server --open demo/

If your demo itself is a SPA, you can also specify the app-index option:

npx owc-dev-server --app-index demo/index.html --open

Auto reload

You can let the server automatically reload the browser on file changes by using the watch flag. This requires the --app-index flag to be set as well. Note that this does not work on IE11 or Edge.

npx owc-dev-server --app-index demo/index.html --open --watch

Additional configs like a proxy

If you need additional configuration for the server you can provide them via a config file .owc-dev-server.config.js.

// example for a proxy middleware for netlify lambda functions
const proxy = require('http-proxy-middleware');

module.exports = function(app) {
  app.use(proxy('/.netlify/functions/', {
    target: 'http://localhost:9000/',
    "pathRewrite": {
      "^/\\.netlify/functions": ""

Command line options

name alias type description
--port -p number The port to use. Default: 8080
--hostname -h string The hostname to use. Default: localhost
--open -o string/boolean Opens the default browser on the given path, the app index or default /
--app-index -a string The app's index.html file. When set, serves the index.html for non-file
--watch -w boolean Whether to reload the browser on file changes. (Does not work on IE/Edge)
--root-dir -r string The root directory to serve files from. Defaults to the project root.
--modules-dir -m string Directory to resolve modules from. Default: node_modules
--config-file -c string File with additional config. Default: .owc-dev-server.config.js
--help none none See all options
Last Updated: 1/27/2019, 3:38:18 PM