Modern applications often need to communicate with each other.
For example, an online store may need to notify an inventory system when a customer places an order. Similarly, a payment platform may need to inform an application when a payment is completed.
One application needs a way to tell another application that something has happened.
This is where webhooks become useful.
A webhook is a way for one application to automatically send data to another application when a specific event occurs. Instead of repeatedly asking whether something has changed, the receiving application is notified when the event happens.
In this article, we’ll explain what a webhook is, how webhooks work, how they differ from APIs, and where they are commonly used.
What Is a Webhook?
A webhook is an automated HTTP-based notification sent from one application to another when a specific event occurs.
The basic idea is:
An Event Happens
↓
Application Sends HTTP Request
↓
Another Application Receives Data
For example, imagine a payment is successfully completed.
Without a webhook, an application may repeatedly ask:
Has the payment been completed?
With a webhook:
Payment Completed
↓
Payment Platform
↓
Webhook Sent
↓
Your Application
Your application receives the notification automatically.
Therefore, webhooks are often described as event-driven communication between applications.
How Does a Webhook Work?
A webhook usually requires two applications:
- The sending application
- The receiving application
The receiving application provides a URL where it can receive webhook requests.
For example:
https://yourapp.com/webhooks/payment
The sending application stores this URL.
When a configured event occurs, the sending application makes an HTTP request to that URL.
The process looks like this:
Event Happens
↓
Sending Application
↓
HTTP POST Request
↓
Webhook URL
↓
Receiving Application
The receiving application can then process the data.
A Simple Real-World Example
Imagine you have an e-commerce application.
A customer completes a payment.
The flow might look like this:
Customer
↓
Completes Payment
↓
Payment Platform
↓
Payment Success Event
↓
Webhook Sent
↓
Your Application
↓
Update Order Status
The application does not need to continuously ask the payment platform whether the payment has been completed.
Instead, it receives an event notification.
Webhook vs API: What Is the Difference?
Webhooks and APIs are related because both help applications communicate.
However, they usually work differently.
API
With a traditional API request, your application asks for information.
For example:
Your Application
↓
"Has the Payment Been Completed?"
↓
Payment API
↓
Response
Your application initiates the request.
This approach is often called pull-based communication.
Webhook
With a webhook, another application sends information when an event occurs.
For example:
Payment Completed
↓
Payment Platform
↓
"Here Is the Payment Event"
↓
Your Application
The sending application initiates the notification.
This is often called push-based communication.
API vs Webhook Comparison
| API | Webhook |
|---|---|
| Your application requests information | Another application sends information |
| Pull-based | Push-based |
| Can be used whenever data is needed | Usually triggered by an event |
| The client initiates the request | The event source initiates the request |
| May require repeated polling | Reduces the need for polling |
In practice, many modern systems use both APIs and webhooks.
For example, a webhook may notify your application about an event, and your application may then use an API to retrieve additional information.
Why Are Webhooks Useful?
Webhooks allow applications to react quickly to events.
For example, they can be used when:
- A payment is completed
- A user signs up
- An order is created
- A subscription is cancelled
- A file is uploaded
- A deployment finishes
- A message is received
The general flow is:
Event
↓
Webhook
↓
Application Reacts
As a result, applications can automate workflows without constantly checking for updates.
Common Webhook Use Cases
Webhooks are used in many types of applications.
1. Payment Notifications
A payment provider can notify an application when:
- A payment succeeds
- A payment fails
- A refund is issued
- A subscription changes
For example:
Payment Event
↓
Webhook
↓
Update Order
2. E-Commerce Automation
An online store can send a webhook when:
- A new order is created
- An order is cancelled
- Inventory changes
- A shipment is delivered
Another system can automatically process the event.
3. Git Repository Events
Development platforms can send webhooks when:
- Code is pushed
- A pull request is opened
- A pull request is merged
- A new issue is created
For example:
Code Pushed
↓
Webhook
↓
CI/CD System
↓
Run Tests
4. CI/CD Automation
Webhooks are commonly used in software deployment workflows.
For example:
Code Updated
↓
Webhook Triggered
↓
Build Process Starts
↓
Tests Run
↓
Application Deployed
This allows deployment systems to react automatically to code changes.
5. Messaging and Notifications
A messaging service can send a webhook when a new message arrives.
For example:
New Message
↓
Webhook
↓
Application
↓
Process Message
What Data Does a Webhook Send?
Webhook data is often sent in the request body.
A common format is JSON.
For example:
{
"event": "payment.completed",
"paymentId": "pay_12345",
"amount": 500,
"currency": "INR"
}
The receiving application reads the request and processes the event.
For example:
Webhook Request
↓
Read Event Type
↓
Validate Request
↓
Process Event
↓
Return Response
The exact data format depends on the sending service.
What Is a Webhook Endpoint?
A webhook endpoint is the URL that receives webhook requests.
For example:
https://example.com/webhooks/orders
When the configured event occurs, the sending application makes a request to this endpoint.
The endpoint might be:
POST /webhooks/orders
A server-side application then handles the request.
For example, a Node.js application may have a route similar to:
app.post("/webhooks/orders", (req, res) => {
console.log(req.body);
res.status(200).send("Webhook received");
});
The endpoint receives the event data and responds to the sender.
What Happens After a Webhook Is Received?
Receiving a webhook is only the first step.
A typical process looks like this:
Receive Webhook
↓
Verify Sender
↓
Validate Data
↓
Identify Event
↓
Process Event
↓
Update Application
For example:
Payment Completed
↓
Webhook Received
↓
Verify Signature
↓
Find Order
↓
Update Payment Status
↓
Send Confirmation
This allows applications to automate actions based on external events.
How Do You Secure a Webhook?
Webhook endpoints are publicly accessible in many systems.
Therefore, security is extremely important.
A malicious user could try to send fake requests to a webhook endpoint.
For this reason, applications should verify that the request actually came from the expected service.
1. Use HTTPS
Webhook endpoints should use HTTPS.
For example:
https://example.com/webhooks/payment
HTTPS encrypts data while it travels between applications.
Therefore, sensitive event data is better protected during transmission.
2. Verify Webhook Signatures
Many webhook providers include a signature with each request.
The receiving application can use this signature to verify the request.
The general idea is:
Webhook Request
↓
Signature Included
↓
Application Verifies Signature
↓
Valid?
↙ ↘
No Yes
↓ ↓
Reject Process
Signature verification helps reduce the risk of accepting forged webhook requests.
The exact verification method depends on the provider.
3. Validate the Request Data
Even after verifying the sender, applications should validate the received data.
For example, verify:
- Expected event type
- Required fields
- Data format
- Data types
The process can look like:
Webhook Received
↓
Validate Data
↓
Valid?
↙ ↘
No Yes
↓ ↓
Reject Process
Validation helps prevent unexpected data from causing application problems.
4. Respond Quickly
Many webhook providers expect a response within a specific time.
If processing takes too long, the provider may consider the request unsuccessful.
A common approach is:
Receive Webhook
↓
Validate
↓
Return Success Response
↓
Process Heavy Work Separately
For example, time-consuming tasks can be placed in a background queue.
This allows the webhook endpoint to respond quickly.
5. Handle Duplicate Webhooks
A webhook event may sometimes be delivered more than once.
For example:
Payment Completed
↓
Webhook Sent
↓
Response Not Received
↓
Webhook Sent Again
Therefore, webhook processing should be designed to handle duplicates safely.
This property is often called idempotency.
For example, if an event has already been processed:
Webhook Event
↓
Check Event ID
↓
Already Processed?
↙ ↘
Yes No
↓ ↓
Ignore Process
This prevents duplicate events from creating duplicate orders or repeated actions.
6. Handle Failed Webhook Deliveries
Webhook requests can fail because of:
- Network problems
- Server errors
- Temporary outages
- Timeouts
Many webhook providers retry failed deliveries.
Therefore, applications should be prepared for repeated requests.
A reliable design may include:
Webhook
↓
Temporary Failure
↓
Retry
↓
Application Available
↓
Process Event
Additionally, applications should monitor failed webhook events.
Webhooks and Background Queues
A webhook may trigger work that takes several seconds or minutes.
For example:
- Generating a report
- Processing a file
- Sending multiple notifications
- Updating several systems
Instead of performing everything directly inside the webhook request:
Webhook
↓
Heavy Processing
↓
Slow Response
a better approach may be:
Webhook
↓
Validate
↓
Add Job to Queue
↓
Return Response
↓
Background Worker Processes Job
This improves reliability and responsiveness.
Webhook Retry Flow
A reliable webhook system should expect failures.
For example:
Webhook Sent
↓
Application Responds?
↙ ↘
No Yes
↓ ↓
Retry Success
The exact retry strategy depends on the sending provider.
However, receiving applications should be designed to safely handle retries and duplicate deliveries.
Webhook Architecture Example
A modern webhook architecture may look like this:
External Service
↓
Webhook Request
↓
API Gateway
↓
Webhook Endpoint
↓
Verify Signature
↓
Validate Event
↓
Message Queue
↓
Background Worker
↓
Database / Other Services
This architecture separates receiving the event from processing complex tasks.
As a result, the webhook endpoint can remain fast and reliable.
Polling vs Webhooks
Polling means repeatedly asking a service for updates.
For example:
Application
↓
Any Updates?
↓
No
↓
Wait
↓
Any Updates?
↓
No
Eventually:
Any Updates?
↓
Yes
This can generate unnecessary requests.
Webhooks work differently:
Event Happens
↓
Service Sends Notification
↓
Application Processes Event
Therefore, webhooks can reduce unnecessary polling when an event-driven approach is suitable.
Advantages of Webhooks
Webhooks provide several benefits.
Real-Time Notifications
Applications can react soon after an event occurs.
Reduced Polling
The receiving application does not need to repeatedly request updates.
Automation
Events can automatically trigger workflows.
Better Integration
Different applications can communicate more efficiently.
Scalable Event Processing
Webhooks can work with queues and background workers.
Challenges of Webhooks
Webhooks also introduce challenges.
For example:
- Requests can fail.
- Events may be delivered multiple times.
- Events may arrive unexpectedly.
- Endpoints must be secured.
- Processing must handle retries.
- Event ordering may not always be guaranteed.
Therefore, production webhook systems should be designed with reliability in mind.
Webhook Best Practices
When building a webhook system, follow these practices:
Use HTTPS
Protect webhook data in transit.
Verify Signatures
Confirm that requests come from the expected sender.
Validate Data
Check event types and required fields.
Respond Quickly
Avoid performing heavy processing inside the request.
Use Background Jobs
Move time-consuming work to queues and workers.
Handle Duplicate Events
Use event IDs and idempotent processing.
Expect Retries
Design the system to safely process repeated deliveries.
Monitor Failures
Track failed events and webhook errors.
Log Important Information
Record event IDs, timestamps, and processing results.
A Complete Webhook Flow
Here is a simplified end-to-end webhook process:
Event Happens
↓
Sending Application
↓
HTTP POST Request
↓
Webhook Endpoint
↓
Verify Signature
↓
Validate Data
↓
Check Event ID
↓
Already Processed?
↙ ↘
Yes No
↓ ↓
Ignore Add to Queue
↓
Return Success
↓
Background Worker
↓
Process Event
This approach provides a good foundation for reliable webhook processing.
Webhook vs API: Which Should You Use?
The answer depends on the use case.
Use an API when your application needs to request data.
For example:
Get User Information
Get Product Details
Get Account Balance
Use a webhook when your application needs to know that something happened.
For example:
Payment Completed
Order Created
User Registered
Deployment Finished
In many systems, both work together.
A webhook can notify your application that an event happened.
Then an API can provide additional details if needed.
Final Thoughts: What Is a Webhook?
A webhook is an automated way for one application to notify another application when a specific event occurs.
Instead of repeatedly asking:
“Did something happen?”
your application receives a notification when it does.
The basic flow is:
Event → Webhook Request → Your Endpoint → Process Event
Webhooks are widely used for payments, e-commerce, software development, CI/CD pipelines, notifications, and application integrations.
Conclusion
Webhooks are an important part of modern application communication.
They allow systems to react to events automatically and reduce the need for constant polling.
However, reliable webhook systems require more than simply creating an HTTP endpoint.
Applications should verify webhook signatures, validate incoming data, handle retries, prevent duplicate processing, and move heavy work to background systems.
By following these practices, developers can build secure and reliable event-driven integrations.
The key idea is simple:
An event happens, and another application is automatically notified.
