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Developing the Frontend UI

This guide explains how to run the Browsertrix frontend development server with Yarn.

Instead of rebuilding the entire frontend image to view your UI changes, you can use the included local development server to access the frontend from your browser. This setup is ideal for rapid UI development that does not rely on any backend changes.


1. Browsertrix API backend already in a Kubernetes cluster

The frontend development server requires an existing backend that has been deployed locally or is in production. See Deploying Browsertrix.

2. Node.js ≥18 and Yarn 1

To check if you already have Node.js installed, run the following command in your command line terminal:

node --version

You should see a version number like v18.12.1. If you see a command line error instead of a version number, install Node.js before continuing.

What if my other project requires a different version of Node.js?

You can use Node Version Manager to install multiple Node.js versions and switch versions between projects.

To check your Yarn installation:

yarn --version

You should see a version number like 1.22.19. If you do not, install or upgrade Yarn.


From the command line, change your current working directory to /frontend:

cd frontend


From this point on, all commands in this guide should be run from the frontend directory.

Install UI dependencies:

yarn install

Copy environment variables from the sample file:

cp sample.env.local .env.local

Update API_BASE_URL in .env.local to point to your backend API host. For example:



This setup assumes that your API endpoints are available under /api, which is the default configuration for the Browsertrix backend.

If connecting to a local deployment cluster, set API_BASE_URL to:

Port when using Minikube (on macOS)

When using Minikube on macOS, the port will not be 30870. Instead, Minikube opens a tunnel to a random port, obtained by running minikube service browsertrix-cloud-frontend --url in a separate terminal.

Set API_BASE_URL to provided URL instead, eg. API_BASE_URL=<TUNNEL_PORT>

Start the frontend development server:

yarn start

This will open localhost:9870 in a new tab in your default browser.

Saving changes to files in src will automatically reload your browser window with the latest UI updates.

To stop the development server type Ctrl+C into your command line terminal.


yarn <name>
start runs app in development server, reloading on file changes
test runs tests in chromium with playwright
build-dev bundles app and outputs it in dist directory
build bundles app, optimized for production, and outputs it to dist
lint find and fix auto-fixable javascript errors
format formats js, html, and css files
localize:extract generate XLIFF file to be translated
localize:build output a localized version of strings/templates


Tests assertions are written in Chai.

To watch for file changes while running tests:

yarn test --watch

To run tests in multiple browsers:

yarn test --browsers chromium firefox webkit


Wrap text or templates in the msg helper to make them localizable:

// import from @lit/localize:
import { msg } from "@lit/localize";

// later, in the render function:
render() {
  return html`
      ${msg("Click me")}

Entire templates can be wrapped as well:

render() {
  return msg(html`
    <p>Click the button</p>
    <button>Click me</button>


To add new languages:

  1. Add BCP 47 language tag to targetLocales in lit-localize.json
  2. Run yarn localize:extract to generate new .xlf file in /xliff
  3. Provide .xlf file to translation team
  4. Replace .xlf file once translated
  5. Run yarn localize:build bring translation into src