What is a Webhook?
A webhook is an HTTP callback that sends real-time data from one application to another when a specific event occurs. Think of it as a notification system for applications.
Instead of your application constantly asking "Did anything happen yet?" (polling), webhooks flip the model: the source application tells you "Hey, something just happened!" by sending an HTTP POST request to a URL you specify.
How Webhooks Work
Webhooks follow a simple three-step process:
Register Your Webhook URL
You provide a URL endpoint to the service you want to receive events from. This is where the service will send HTTP POST requests when events occur.
Event Occurs
When something happens in the source application (e.g., a payment succeeds, a user signs up, a file is uploaded), it triggers the webhook.
Receive and Process
The service sends an HTTP POST request to your URL with event data in the request body. Your application receives and processes this data.
Example Webhook Payload
POST /webhooks/stripe HTTP/1.1
Host: api.yourapp.com
Content-Type: application/json
Stripe-Signature: t=1234567890,v1=abc123...
{
"id": "evt_1234567890",
"type": "payment_intent.succeeded",
"data": {
"object": {
"id": "pi_1234567890",
"amount": 2000,
"currency": "usd",
"status": "succeeded"
}
}
}Webhooks vs API Polling
Understanding the difference between webhooks and traditional API polling is crucial for choosing the right approach.
| Aspect | Webhooks (Push) | API Polling (Pull) |
|---|---|---|
| Communication Model | Event-driven, real-time | Request-response, periodic |
| Latency | Milliseconds | Seconds to minutes |
| Resource Usage | Low (only when events occur) | High (constant requests) |
| Complexity | Requires public endpoint | Simpler to implement |
| Best For | Real-time notifications | Periodic data sync |
Real-World Webhook Examples
Payment Processing
Stripe sends a webhook when a payment succeeds, fails, or requires additional authentication. Your app can immediately update order status and send confirmation emails.
CI/CD Pipelines
GitHub sends webhooks when code is pushed, pull requests are opened, or issues are created. This triggers automated builds and deployments.
E-commerce
Shopify notifies your app when orders are created, products are updated, or inventory changes. Keep your systems in sync automatically.
Communication
Twilio sends webhooks for incoming SMS messages, call status updates, and delivery receipts. Build real-time communication features.
When Should You Use Webhooks?
✓ Use Webhooks When:
You need real-time notifications
Events must be processed immediately (payments, alerts, time-sensitive actions)
Reducing API call overhead
Polling would waste resources checking for infrequent events
Building integrations
Connecting multiple systems that need to stay synchronized
Event-driven architecture
Microservices need to react to changes in other services
✗ Avoid Webhooks When:
You can't expose a public endpoint
Security policies prevent incoming HTTP requests (use polling or message queues)
You need to fetch large datasets
Webhooks are for notifications, not bulk data transfer (use batch APIs)
Real-time isn't critical
Hourly or daily sync is sufficient (polling is simpler)
Frequently Asked Questions
Are webhooks secure?
Webhooks can be secure when implemented correctly. Most services sign webhook payloads using HMAC signatures, allowing you to verify requests are authentic. Always validate signatures, use HTTPS, and implement rate limiting.
What happens if my webhook endpoint is down?
Most webhook providers implement retry logic with exponential backoff. They'll attempt to deliver the webhook multiple times over hours or days. After max retries, the webhook may be marked as failed. Always implement proper error handling and monitoring.
Can I test webhooks locally?
Yes! You can use localhost tunneling tools like hookVM's CLI, ngrok, or localtunnel to expose your local development server to the internet temporarily. This allows you to receive webhooks on localhost for testing.
Do webhooks guarantee delivery?
Webhooks provide at-least-once delivery, meaning you might receive the same webhook multiple times. Implement idempotency in your webhook handlers to safely process duplicate events. Most providers retry failed deliveries but don't guarantee success.
Ready to Work with Webhooks?
Now that you understand what webhooks are, learn how to implement them securely and reliably in production.