LaunchDarkly developer toolbar

Overview

This topic describes how to install and use the LaunchDarkly developer toolbar. You can install and configure the toolbar directly in your codebase, and use it in your browser during local development.

The toolbar lets you:

• View a list of feature flags in use for your project, and easily override values locally to test application behavior for flag variations
• Listen to incoming events, including flag evaluation events
• Easily identify missing feature flags and link to your LaunchDarkly project so you can create them

Prerequisites

To begin using the developer toolbar, you need:

• A front-end application using React
• A client-side ID for your LaunchDarkly environment

Installation

Depending on your package manager, install the @launchdarkly/toolbar package using one of the following methods:

$
npm install @launchdarkly/toolbar@next

Mode options

The developer toolbar supports running in two different modes:

• SDK mode: Integrates with your LaunchDarkly SDK for local flag overrides and testing
• Dev server mode: Connects to a LaunchDarkly CLI dev server for flag browsing and real-time updates

SDK mode is the default mode for the toolbar. The toolbar switches to dev server mode only if you provide devServerUrl. Generally, we recommend SDK mode.

Available features by mode

Set up SDK mode

SDK mode integrates directly with your LaunchDarkly client, allowing you to:

• Override flag values locally without affecting other members
• Test different flag variations instantly
• Work offline or with any LaunchDarkly environment

Setup requires the following steps:

1. Create a FlagOverridePlugin instance
2. (Optional) Create an EventInterceptionPlugin instance
3. Pass the plugin into your LaunchDarkly SDK’s plugins array
4. Pass the same plugin instance into the LaunchDarklyToolbar component
5. Wrap your app with the LDProvider

Here’s how to set up SDK mode:

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import { useEffect, useState } from 'react';
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import { asyncWithLDProvider } from 'launchdarkly-react-client-sdk';
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import { 
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  LaunchDarklyToolbar,
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  FlagOverridePlugin,
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  EventInterceptionPlugin 
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} from '@launchdarkly/toolbar';
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// Create the plugin instances
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const flagOverridePlugin = new FlagOverridePlugin({
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  storageNamespace: 'my-app-overrides', // Optional: customize storage key
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});
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const eventInterceptionPlugin = new EventInterceptionPlugin({
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  eventCapacity: 250, // Maximum events to store (default: 150)
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  enableLogging: true, // Console logging for debugging (default: false)
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});
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function App() {
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  const [LDProvider, setLDProvider] = useState(null);
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  useEffect(() => {
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    const initializeLD = async () => {
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      const Provider = await asyncWithLDProvider({
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        clientSideID: 'enter-your-client-side-id',
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        context: { key: 'context-key-123abc', name: 'Sandy Smith' },
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        options: {
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          // Pass the plugins to the SDK
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          plugins: [flagOverridePlugin, eventInterceptionPlugin],
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        },
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      });
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      setLDProvider(() => Provider);
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    };
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    initializeLD();
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  }, []);
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  if (!LDProvider) {
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    return <div>Loading LaunchDarkly...</div>;
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  }
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  return (
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    <LDProvider>
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      <div>
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        <h1>My App</h1>
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        {/* Pass the same plugin instances to the toolbar */}
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        <LaunchDarklyToolbar
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          flagOverridePlugin={flagOverridePlugin}
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          eventInterceptionPlugin={eventInterceptionPlugin}
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        />
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      </div>
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    </LDProvider>
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  );
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}

Set up dev server mode

If your team uses the LaunchDarkly CLI dev server, start it with CORS enabled:

$
ldcli dev-server start --project your-project --cors-enabled true

Then connect the toolbar by passing in the URL of the CLI dev server:

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import { LaunchDarklyToolbar } from '@launchdarkly/toolbar';
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function App() {
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  return (
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    <div>
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      <h1>My App</h1>
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      <LaunchDarklyToolbar devServerUrl="http://localhost:8765" />
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    </div>
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  );
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}

Properties

You can set the following properties to personalize the toolbar.

Flag override plugin

The flag override plugin enables flag overrides and testing:

Event interception plugin

The event interception plugin enables Events tab functionality:

Base LaunchDarkly URL

You can use the base LaunchDarkly URL for link generation, such as to create a missing feature flag:

LaunchDarkly dev server URL

You can use the URL of your LaunchDarkly dev server to enable dev server mode:

Toolbar position

You can set the toolbar position on your screen:

Project key

You can use a project key in multi-project setups (dev server mode only):

Polling interval

You can set the polling interval for dev server updates (dev server mode only):

Visibility control

The toolbar provides a global API for show/hide control:

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// Toggle visibility
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window.ldToolbar.toggle();
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// Enable/disable explicitly
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window.ldToolbar.enable();
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window.ldToolbar.disable();
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// Check current status
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window.ldToolbar.status(); // returns true/false