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This guide walks you through using ngrok to receive Svix incoming webhooks on your localhost app. By integrating ngrok with Svix, you can:
  • Develop and test Svix webhooks locally without deploying to a public environment or setting up HTTPS.
  • Inspect and troubleshoot requests from Svix in real time via the inspection UI and API.
  • Modify and replay Svix webhook requests with a single click instead of reproducing events manually in your Svix account.
  • Secure your app with Svix 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 Svix.

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3. Configure Svix to send webhooks

Svix can send incoming webhook requests to your app when events occur. To register for those events:
  • Sign in to the Svix Dashboard.
  • In the left menu, click Incoming Webhooks and Add Endpoint.
  • Enter your ngrok URL in Endpoint URL (for example, https://1a2b-3c4d-5e6f-7g8h-9i0j.ngrok.app).
  • Under Message Filtering, select the events you want (for example, endpoint and message) and click Create.
  • On the webhook page, open the Testing tab and click Send Example.
Confirm your localhost app receives the request and logs both headers and body in the terminal.

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Run webhooks with Svix and ngrok

Svix sends different request body contents depending on the event. To trigger more calls:
  • In the Svix Dashboard, click Consumer Applications and your app (create one if needed).
  • Click Preview App Portal and Add Endpoint.
  • On New Endpoint, use use Svix Play or enter a URL in Endpoint URL, then click Create.
Confirm your localhost app receives the request. You can verify delivery under Incoming Webhooks, Logs, in the Svix dashboard.

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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 Svix 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:
  • In the Svix Dashboard, go to Incoming Webhooks, click your webhook URL, and under Signing Secret click the eye icon and copy the value.
  • Create a Traffic Policy file named svix_policy.yml. Replace {your webhook secret} with the value you copied: 
    on_http_request:
  - actions:
      - type: verify-webhook
        config:
          provider: svix
          secret: "{your webhook secret}"
  • Restart ngrok with the policy file: 
    ngrok http 3000 --traffic-policy-file svix_policy.yml
  • Create a new endpoint or send a test from the Svix dashboard to trigger the webhook.
Your app should receive the request and log it in the terminal.