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LaunchDarkly Webhooks

This guide covers how to use ngrok to integrate your localhost app with LaunchDarkly by using Webhooks. LaunchDarkly webhooks can be used to notify an external application whenever specific events occur in your LaunchDarkly account.

By integrating ngrok with LaunchDarkly, you can:

  • Develop and test LaunchDarkly webhooks locally, eliminating the time in deploying your development code to a public environment and setting it up in HTTPS.
  • Inspect and troubleshoot requests from LaunchDarkly in real-time via the inspection UI and API.
  • Modify and Replay LaunchDarkly Webhook requests with a single click and without spending time reproducing events manually in your LaunchDarkly account.
  • Secure your app with LaunchDarkly validation provided by ngrok. Invalid requests are blocked by ngrok before reaching your app.

Step 1: Start your app

For this tutorial, we'll use the sample NodeJS app available on GitHub.

To install this sample, run the following commands in a terminal:

git clone
cd ngrok-webhook-nodejs-sample
npm install

This will get the project installed locally.

Now you can launch the app by running the following command:

npm start

The app runs by default on port 3000.

You can validate that the app is up and running by visiting http://localhost:3000. The application logs request headers and body in the terminal and responds with a message in the browser.

Step 2: Launch ngrok

Once your app is running successfully on localhost, let's get it on the internet securely using ngrok!

  1. If you're not an ngrok user yet, just sign up for ngrok for free.

  2. Download the ngrok agent.

  3. Go to the ngrok dashboard and copy your Authtoken.
    Tip: The ngrok agent uses the auth token to log into your account when you start a tunnel.

  4. Start ngrok by running the following command:

    ngrok http 3000
  5. ngrok will display a URL where your localhost application is exposed to the internet (copy this URL for use with LaunchDarkly). ngrok agent running

Step 3: Integrate LaunchDarkly

To register a webhook on your LaunchDarkly account follow the instructions below:

  1. Access the LaunchDarkly App and sign in using your LaunchDarkly account.

  2. On the left menu, click Integrations.

  3. On the Integrations page, search for webhooks and then click Add integration for the Webhooks tile.

  4. On the Create a new webhook popup, enter a name in the NAME field, and enter the URL provided by the ngrok agent to expose your application to the internet in the URL field (i.e. URL

  5. On the Create a new webhook popup, click Sign this webhook and copy the value of the Secret provided by LaunchDarkly. Tip: You will use the Secret value later to add more security to your webhook calls. See Secure webhook requests.

  6. Click the I have read and agree to the Integration Terms and Conditions checkbox, and then click Save settings.

After you save the webhook, LaunchDarkly sends a request to your application. Confirm your localhost app receives the POST notification and logs both headers and body in the terminal.

Run Webhooks with LaunchDarkly and ngrok

LaunchDarkly sends different request body contents depending on the event that is being triggered. You can trigger new calls from LaunchDarkly to your application by following the instructions below.

  1. On the LaunchDarkly dashboard, click Segments on the left menu and then click Create segment.

  2. On the Create a segment popup, enter a Name for the segment, and then click Save segment.

    Confirm your localhost app receives the create-project event notification and logs both headers and body in the terminal.

Inspecting requests

When you launch the ngrok agent on your local machine, you can see two links: one for the tunnel to your app (it ends up in unless you're using custom domains) and a local URL for the Web Interface (a.k.a Request Inspector).

The Request Inspector shows all the requests made through your ngrok tunnel to your localhost app. When you click on a request, you can see details of both the request and the response.

Seeing requests is an excellent way of validating the data sent to and retrieved by your app via the ngrok tunnel. That alone can save you some time dissecting and logging HTTP request and response headers, methods, bodies, and response codes within your app just to confirm you are getting what you expect.

To inspect LaunchDarkly's webhooks call, launch the ngrok web interface (i.e. and then click one of the requests sent by LaunchDarkly.

From the results, review the response body, header, and other details:

ngrok Request Inspector

Replaying requests

The ngrok Request Inspector provides a replay function that you can use to test your code without the need to trigger new events from LaunchDarkly. To replay a request:

  1. In the ngrok inspection interface (i.e. http://localhost:4040), select a request from LaunchDarkly.

  2. Click Replay to execute the same request to your application or select Replay with modifications to modify the content of the original request before sending the request.

  3. If you choose to Replay with modifications, you can modify any content from the original request. For example, you can modify the name field inside the body of the request.

  4. Click Replay.

Verify that your local application receives the request and logs the corresponding information to the terminal.

Secure webhook requests

The ngrok signature webhook verification feature allows ngrok to assert that requests from your LaunchDarkly webhook are the only traffic allowed to make calls to your localhost app.

Note: This ngrok feature is limited to 500 validations per month on free ngrok accounts. For unlimited, upgrade to Pro or Enterprise.

This is a quick step to add extra protection to your application.

  1. Restart your ngrok agent by running the command, replacing {your webhook secret} with the value you have copied before (See Integrate ngrok and LaunchDarkly.):

    ngrok http 3000 --verify-webhook LAUNCH_DARKLY --verify-webhook-secret {your webhook secret}
  2. Access the LaunchDarkly App and create a new segment.

Verify that your local application receives the request and logs information to the terminal.