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This guide explains how to use ngrok to receive Amazon SNS topic notifications on your localhost app. By integrating ngrok with Amazon SNS, you can:
  • Develop and test Amazon SNS webhooks locally without deploying to a public environment or setting up HTTPS.
  • Inspect and troubleshoot requests from Amazon SNS in real time via the inspection UI and API.
  • Modify and replay Amazon SNS webhook requests with a single click instead of reproducing notifications manually in your SNS topic.
  • Secure your app with Amazon SNS 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 Amazon SNS.

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3. Configure Amazon SNS to send webhooks

Amazon SNS sends notifications to an HTTP/S endpoint that you subscribe to a topic. Using a standard SNS topic, follow AWS’s documentation for subscribing an HTTPS endpoint to an SNS topic, and set the following:
  • Protocol: HTTPS.
  • Endpoint: your ngrok URL (for example, https://1a2b-3c4d-5e6f-7g8h-9i0j.ngrok.app).
After you create the subscription, SNS sends a SubscriptionConfirmation request to your app. Copy the SubscribeURL value from the request body your app logs, then confirm the subscription in SNS using that URL. The subscription status changes to confirmed once you do.

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Run webhooks with Amazon SNS and ngrok

Publishing a message to your topic triggers your HTTPS subscription. To trigger a webhook call, publish a message to the topic from SNS. Confirm your app receives the notification and logs the 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.

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Secure webhook requests

ngrok can verify that incoming requests are from your Amazon SNS topic 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:
  • In the AWS console, open the Amazon SNS Dashboard and click Topics.
  • Open your topic and copy the value of Topic owner.
  • Create a Traffic Policy file named amazon_sns_policy.yml. Replace {Topic owner} with the value you copied:
  • Restart ngrok with the policy file:
  • Publish a new message to your topic from the AWS console.
Your app should receive the request and log it in the terminal.