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If you don’t see your preferred webhook provider, you can request support for it.
This guide shows you how to use ngrok to receive Mailchimp webhooks on your localhost app. By integrating ngrok with Mailchimp, you can:
  • Develop and test Mailchimp webhooks locally without deploying to a public environment or setting up HTTPS.
  • Inspect and troubleshoot requests from Mailchimp in real time via the inspection UI and API.
  • Modify and replay Mailchimp webhook requests with a single click instead of reproducing events manually in your Mailchimp account.
  • Secure your app with Mailchimp webhook validation provided by ngrok. Invalid requests are blocked by ngrok before reaching your app.

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What you’ll need

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1. Start your app

For this tutorial, you can use the sample Node.js app on GitHub. To install the sample, run the following in a terminal:
Then start the app:
The app runs on port 3000 by default. You can confirm it’s running by visiting http://localhost:3000. The app logs request headers and body in the terminal and shows a message in the browser.

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2. Expose your app with ngrok

Once your app is running locally, you’re ready to put it online securely using ngrok.
The ngrok agent uses your authtoken to authenticate when you start a tunnel.
  • Start ngrok:
  • Copy the URL ngrok displays. Your app is now exposed at that URL for use with Mailchimp.

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3. Configure Mailchimp to send webhooks

Follow Mailchimp’s documentation for creating an audience webhook, and set the following:
  • Callback URL: your ngrok URL (for example, https://1a2b-3c4d-5e6f-7g8h-9i0j.ngrok.app).
  • Actions: choose which audience updates trigger the webhook.
When you save the webhook, Mailchimp sends a verification request to your callback URL. Confirm your localhost app receives it and logs both headers and body in the terminal.

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Run webhooks with Mailchimp and ngrok

Mailchimp sends different request body contents depending on the audience and the actions you selected. To trigger a call, cause one of those updates in your audience, such as adding a new subscriber.
If the email is not on your contact list, you may need to import the contact first.
Confirm your localhost app receives the event and logs both headers and body in the terminal.

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Inspecting requests

ngrok’s Traffic Inspector captures all requests made through your ngrok endpoint to your localhost app. Select any request to view detailed information about both the request and response.
To avoid exposing secrets, accounts only collect traffic metadata by default. You must enable full capture in the Traffic Inspector section of your account settings to capture complete request and response data.
Use the traffic inspector to:
  • Validate webhook payloads and response data
  • Debug request headers, methods, and status codes
  • Troubleshoot integration issues without adding logging to your app

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Replaying requests

Test your webhook handling code without triggering new events from your service using the Traffic Inspector’s replay feature:
  1. Send a test webhook from your service to generate traffic in your Traffic Inspector.
  2. Select the request you want to replay in the traffic inspector.
  3. Choose your replay option:
    • Click Replay to send the exact same request again
    • Select Replay with modifications to edit the request before sending
  4. (Optional) Modify the request: Edit any part of the original request, such as changing field values in the request body.
  5. Send the request by clicking Replay.
Your local application will receive the replayed request and log the data to the terminal.