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This guide shows you how to use ngrok to receive MongoDB webhooks on your localhost app. By integrating ngrok with MongoDB Atlas, you can:
  • Develop and test MongoDB webhooks locally without deploying to a public environment or setting up HTTPS.
  • Inspect and troubleshoot requests from MongoDB in real time via the inspection UI and API.
  • Modify and replay MongoDB webhook requests with a single click instead of reproducing events manually in your MongoDB account.
  • Secure your app with MongoDB 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: 
git clone https://github.com/ngrok/ngrok-webhook-nodejs-sample.git
cd ngrok-webhook-nodejs-sample
npm install
Then start the app: 
npm start
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: 
    ngrok http 3000
  • Copy the URL ngrok displays. Your app is now exposed at that URL for use with MongoDB.

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3. Configure MongoDB to send webhooks

MongoDB can send webhook requests to your app when events occur in your project. To register for those events:
If you don’t have a project, create one first.
  • Click the bell icon below your name to open project alerts.
  • On Project Alerts, click Add New Alert and then Webhooks.
  • On Create a New Alert, under Alert if, select User and User joined the project.
  • Click Add, Webhook, and enter your ngrok URL in Webhook URL (for example, https://1a2b-3c4d-5e6f-7g8h-9i0j.ngrok.app).
  • Enter a value in Webhook Secret (for example, 12345) for use in verification.
  • Click Save.

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Run webhooks with MongoDB and ngrok

MongoDB sends different request body contents depending on the event. To trigger new calls from MongoDB to your app:
  • On your project home page, click the person icon to invite a user.
  • Enter an email in invite new users via email address.
  • After the user registers with MongoDB Atlas, 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 Observability 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.

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Secure webhook requests

ngrok can verify that incoming requests are from your MongoDB webhook so only that traffic reaches your app.
Webhook verification is limited to 500 validations per month on free accounts. If you need more, you can upgrade to Hobbyist or Pay-as-you-go. See TPU Pricing for details.
To add verification:
  • Create a Traffic Policy file named mongodb_policy.yml. Replace {your webhook secret} with the value you entered in Webhook Secret when registering the webhook: 
    on_http_request:
  - actions:
      - type: verify-webhook
        config:
          provider: mongodb
          secret: "{your webhook secret}"
  • Restart ngrok with the policy file: 
    ngrok http 3000 --traffic-policy-file mongodb_policy.yml
  • Invite a new user to your project to trigger the webhook.
Your app should receive the request and log it in the terminal.