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

​
What you’ll need

​
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.

​
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 Alchemy.

​
3. Configure Alchemy to send webhooks

Alchemy can send webhook requests to your app when events occur in your account. To register for those events:
  • Sign in to the Alchemy dashboard.
  • In the left menu, click the Data icon and then Webhooks.
  • On the Webhooks page, click Create Webhook for one of the types (for this tutorial, use Address Activity).
  • Select the Chain and Network you want to monitor, then paste the ngrok URL in the WEBHOOK URL field (for example, https://1a2b-3c4d-5e6f-7g8h-9i0j.ngrok.app).
  • Click Test Webhook and verify your localhost app receives a notification event.
  • Enter your wallet address in Ethereum Address and click Create Webhook.

​
Run webhooks with Alchemy and ngrok

Alchemy sends different request body contents depending on the type of webhook. Because this example uses Address Activity, you need to receive or send tokens to your address to trigger events. To test your webhook:
  • In the Alchemy dashboard, go to Data and Webhooks.
  • In the Address Activity section, click the 3 dots for the webhook you registered and click Send Test Notification.
Confirm your localhost app receives the test event and logs both headers and body in the terminal.

​
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

​
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.

​
Secure webhook requests

ngrok can verify that incoming requests are from your Alchemy 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 Alchemy dashboard, go to Data and Webhooks.
  • In the Address Activity section, click the 3 dots for your webhook and click Signing Key.
  • In the popup, copy the Signing key value and click Close.
  • Create a Traffic Policy file named alchemy_policy.yml. Replace {your signing key} with the value you copied: 
    on_http_request:
  - actions:
      - type: verify-webhook
        config:
          provider: alchemy
          secret: "{your signing key}"
  • Restart ngrok with the policy file: 
    ngrok http 3000 --traffic-policy-file alchemy_policy.yml
After restarting ngrok, the tunnel URL changes. Alchemy does not allow editing webhook URLs, so it’s recommended to create a reserved domain on your ngrok account and run the agent with --domain your-domain.ngrok.app.
  • Test the webhook from the Alchemy dashboard or trigger an event with the Alchemy SDK.
Your app should receive the request and log it in the terminal.