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CircleCI Webhooks

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

By integrating ngrok with CircleCI, you can:

  • Develop and test CircleCI 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 CircleCI in real-time via the inspection UI and API.
  • Modify and Replay CircleCI Webhook requests with a single click and without spending time reproducing events manually in your CircleCI account.
  • Secure your app with CircleCI 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 CircleCI). ngrok agent running

Step 3: Integrate CircleCI

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

  1. Access CircleCI and sign in using your CircleCI account.

  2. On the All Pipelines page, click the name of your pipeline. Tip: If you don't have one, create a new pipeline.

  3. On your pipeline page, click Project Settings and then click Webhooks on the left menu.

  4. On the Webhooks page, click Add Webhook.

  5. On the Add Webhook page, enter a name in the Webhook name field, and in the Receiver URL field enter the URL provided by the ngrok agent to expose your application to the internet (i.e. URL to Publish

  6. Enter MySecretToken in the Secret token field, click the Workflow Completed and Job Completed checkboxes under Events, and then click Add Webhook.

  7. On the Webhooks page, click the name of your webhook, and then click Test Ping Event.

    Confirm your localhost app receives the test-ping event notification and logs both headers and body to the terminal.

Run Webhooks with CircleCI and ngrok

You can trigger new calls from CircleCI to your application by following the instructions below.

  1. Access CircleCI and sign in using your CircleCI account. Tip: If you are at the Project Settings page, click < at the top left corner to return to your pipeline page.

  2. On the Pipeline page, click Rerun workflow from start under the Action column for your pipeline.

    Confirm your localhost app receives event notifications related to the workflow you started 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:

  • The URL to your app (it ends with for free accounts or for paid accounts when not using custom domains)
  • 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 CircleCI's webhooks call, launch the ngrok web interface (i.e., and then click one of the requests sent by CircleCI.

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 CircleCI. To replay a request:

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

  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 CircleCI 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 secret token} with the value you have provided to the Secret token field during your webhook registration (See Integrate ngrok and CircleCI):

    ngrok http 3000 --verify-webhook circleci --verify-webhook-secret {your secret token}
  2. Access CircleCI and Rerun your workflow from start.

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