# About notifications

**Learn how the Notifications service works, when to use it, and how to receive updates from Booking.com without continuously polling the Demand API.**

## The Notifications service

The Notifications service sends updates to your application when subscribed resources change.

* Instead of repeatedly calling Demand API endpoints to check for changes, your HTTPS webhook endpoint is registered and subscribed to a notification topic.
* When a relevant event occurs, Booking.com sends an HTTP POST request containing a notification to your webhook endpoint.


**Notifications complement the Demand API**

* Use notifications to learn when a resource changes.
* If a notification does not contain everything your application needs, use its identifiers to retrieve the latest resource from the Demand API.


### Key concepts

| Concept | Description |
|  --- | --- |
| **Notification** | A message sent to your webhook endpoint when a relevant business event occurs. |
| **Topic** | A category of related notification events that a webhook endpoint can be subscribed to. |
| **Webhook** | Your publicly accessible HTTPS endpoint that receives notifications. |
| **Subscription** | Associates a registered webhook endpoint with a notification topic. |


## Is this guide for you?

Notifications are designed for partners who want to keep their systems synchronised with Booking.com without continuously polling the Demand API.

You can use notifications to:

* Update order information in your platform when a change occurs.
* Trigger traveller communications after an order changes.
* Synchronise internal systems with Booking.com.
* Reduce unnecessary Demand API requests by retrieving resources only when required.


Before integrating Notifications, you should:

| Checklist |
|  --- |
| ☑ | Be integrated with the Demand API. |
| ☑ | Be able to expose a publicly accessible HTTPS endpoint. |
| ☑ | Be able to receive and process HTTP POST requests containing JSON. |
| ☑ | Be able to make follow-up requests to the Demand API when additional information is required. |


## How notifications work

The Notifications service uses a publish-subscribe model to send changes to your application.

1. **An event occurs** — Booking.com detects a relevant business event, such as a car order changing from booked to cancelled.
2. **The event is published** — Booking.com publishes the event to the corresponding notification topic.
3. **A notification is delivered** — If your webhook endpoint is subscribed to that topic, Booking.com sends an HTTP POST request to it.
4. **Your application processes the notification** — Validate the request and use the notification data to update or trigger processing in your application.
5. **Retrieve the latest resource if needed** — If the notification does not contain all the information your application needs, retrieve the latest resource from the Demand API.


![Notifications flow](/assets/notifications-flow.bae9ebc5df951c82c9315324e9036dbdf3da7a1d56a8b733b1e53774c9c4a4f2.7fa386a7.png)

The request to the Demand API is optional. Whether you need it depends on the notification topic and the information your application requires.

## When to use notifications

Use notifications when your application needs to respond to changes without continuously checking the Demand API.

Without notifications, your application might poll an API endpoint at regular intervals to determine whether something has changed.

Polling can:

* Generate API requests when no data has changed.
* Delay processing until the next polling interval.
* Increase the resources required to keep systems synchronised.


Notifications allow your application to react when changes occur.

### Benefits

Notifications can help you:

✓ **Receive timely updates** —  Process changes shortly after Booking.com publishes them.

✓ **Reduce API usage** —  Make Demand API requests when additional resource information is required instead of continuously polling for changes.

✓ **Respond faster**  —  Trigger downstream processes, such as traveller communications, when relevant changes occur.

✓ **Simplify synchronisation**  —  Use notifications to trigger updates between Booking.com and your systems.

## Notifications model

Notifications are lightweight messages that tell your application when a relevant business event occurs.

Depending on the topic, a notification might contain enough information to process the change directly or provide identifiers you can use to retrieve the latest resource from the Demand API.

Notification payloads are topic-specific.

## Topics

Notification events are organised into topics.

A topic represents a category of related business events. Your webhook endpoint is subscribed to the topics for which you want to receive notifications.

### Available topics

Current topics include:

| Topic | Description |
|  --- | --- |
| Car order updates | Receive notifications when relevant information associated with a car order changes. |


Currently, the **Notifications service supports only the Car order updates topic**. Additional topics may be introduced as Notifications support expands to other Booking.com travel services.

## Delivery expectations

Booking.com delivers notifications asynchronously to your registered webhook endpoint using HTTPS `POST` requests.

Keep the following behaviour in mind when designing your integration:

* Delivery order is not guaranteed.
* Delivery can be temporarily delayed by network or service conditions.
* Failed deliveries might be retried.
* Notifications might arrive out of order or more than once.


Design your application so that it does not rely on notification delivery order.

See the [Car order update notifications integration guide](/demand/docs/additional-services/notifications/car-orders-integration-guide) for detailed retry, ordering and duplicate-delivery behaviour.

## Webhook security

Notifications are sent to registered HTTPS webhook endpoints using the authentication mechanism configured for your integration.

Your application must authenticate incoming notification requests before processing them.

See the [Car order update notifications integration guide](/demand/docs/additional-services/notifications/car-orders-integration-guide)  for authentication, request validation and acknowledgement requirements.

## Notifications and the Demand API

Notifications and the Demand API serve different purposes and are designed to work together.

| Notifications | Demand API |
|  --- | --- |
| Informs your application when a relevant event occurs. | Lets your application retrieve or manage resources. |
| Pushes updates to your webhook endpoint. | Responds to requests from your application. |
| Reduces the need for polling. | Provides resource data when your application needs it. |
| Uses topic-specific notification payloads. | Uses the request and response models defined by each API endpoint. |


## What's next

Ready to receive notifications?

* Follow the [Car order update notifications integration guide](/demand/docs/additional-services/notifications/car-orders-integration-guide) to get your webhook registered and subscribed, configure your integration and start processing notifications.


## Related documentation

* [Car order update notification API reference](/demand/docs/additional-services/notifications/notifications/order-update) — Explore the complete notification payload schema and field definitions.
* [Car order latest details](/demand/docs/open-api/3.2-beta/demand-api/orders/details/cars/live) — Optionally retrieve the latest car order details after receiving a notification.