# Development server

Fractal comes with a local development server for running the web UI while you are building your component library.

# Starting the server

You can either start the server using the Fractal CLI tool (if you are using it) or programmatically using Fractal's API.

# Using the CLI tool

You can use the start command from within the root of your project to get the server up and running:

fractal start

You can provide the following (optional) command line options to override the default configuration:

  • -p, --port <port-number> - the port number to use, for example 5000.
  • -t, --theme <theme-name> - the custom theme to use.
  • -s, --sync - whether to use the integrate BrowserSync instance to provide auto-refresh and syncing capabilities
  • -w, --watch - whether to watch components and documentation pages for changes

As an example, the command:

fractal start --watch --port 4000

Would start the preview server at the URL http://localhost:4000 (opens new window) and start watching the filesystem for changes.

# Programmatically

If you wish to start the server programmatically, (often useful for build tool integrations), you can create a new server instance using the fractal.web.server() method and then start and stop it as required:

const server = fractal.web.server();

    console.log(`Fractal server is now running at ${server.url}`);


The Server object returned by the call to fractal.web.server() is a Node EventEmitter and will emit error events (and others) that you can bind to. See the fractal.web API docs for full details.

# BrowserSync integration

The Fractal web server includes a seamless integration with BrowserSync, should you require it.

When enabled, it provides:

  • Auto-reloading of the web UI when files change
  • Re-injecting of static assets (such as stylesheets) when changes are made
  • A network-accessible URL for device testing
  • Syncing of page navigation between tabs
  • Lots more - see the BrowserSync website (opens new window) for details.

BrowserSync can be enabled as a global option, when starting the server via the CLI tool or programmatically:

# Enabling globally

You can configure your Fractal instance to use BrowserSync integration whenever the server is started as follows:

fractal.web.set('server.sync', true);

You can also pass options (opens new window) to the underlying BrowserSync instance using the server.syncOptions property:

fractal.web.set('server.syncOptions', {
    open: true,
    browser: ['google chrome', 'firefox'],
    notify: true

# Using the CLI tool

You can use the --sync option to enable BrowserSync when starting the server:

fractal start --sync

# Programmatically

You can set the sync option to true in the server config object when getting a new server instance:

const server = fractal.web.server({
    sync: true

    console.log(`Local URL: ${server.url}`);
    console.log(`Network URL: ${server.urls.sync.external}`);