Webhook: what they are and why they are useful for APIs

In the world of distributed applications and microservices integration, efficiency in cross-platform communication is an essential requirement. What once required continuous request–response cycles (polling) now takes place through notifications sent in real time from one application to another. 

This is made possible by the webhook mechanism, which allows an update to be automatically sent to the destination application whenever a specific event occurs in the source one. In this way, webhooks make it possible to build an event-driven architecture that ensures the immediacy of real-time communications and the agility of an extremely efficient system, where only the necessary interactions take place.

What is a webhook?

Let’s start with the definitions: a webhook is a client-server communication mechanism, based on user-defined HTTP callbacks, that allows an application to send a real-time notification to another app when a specific event (trigger) occurs.

In essence, when a predefined event occurs in the sending application, it automatically sends an HTTP POST request (the “callback”) to the URL provided by the receiving application (the endpoint).

One of the most classic examples of webhooks is related to e-commerce order management: every time a customer completes a purchase, the e-commerce platform sends a webhook to the warehouse URL, that is, an HTTP POST request containing, in the payload, all the order details. By doing so, the order can be prepared for shipment in a fully automated way, without requiring manual intervention, and above all it can be managed in real time.

How does a webhook work?

To better understand how a webhook works, it can be useful to analyze the three phases of a typical operation:

• Trigger event: a specific event occurs in the web application (for example, a customer places an order on an e-commerce site);
• Callback: the sending application (in this case, the e-commerce platform) sends an automatic notification to a previously configured URL (for example, the warehouse management software) that contains all the new data (the order details);
• Reception and action: the destination application listens on the configured URL. As soon as it receives the HTTP POST request, it extracts the data from the payload and performs the programmed action (for example, creating a new order line in the warehouse or sending a message to the logistics team).

Webhooks are the foundation of many everyday applications: in addition to managing orders on e-commerce platforms, webhooks are used to register new users in databases and add new customers to CRM and email marketing software, as well as to confirm online payments, automatically publish posts on social media, and monitor the operation of websites and platforms in real time.

APIs vs webhooks: what’s the difference?

The main difference between the webhook mechanism and the functioning of traditional APIs, which are based on polling, lies in time management. 

In the traditional (pull) model, the client requests information at regular intervals, for example every minute, and if there are updates it receives the list of new data in response. 

A webhook, on the other hand, allows systems to be updated in real time whenever new data is available, without having to request periodic updates, communicating only when necessary. 

Because of this crucial difference, webhooks are often referred to as an “inverse API”: in fact, it is a “push” mechanism as opposed to the “pull” model of traditional APIs. 

Why are webhooks useful for APIs?

In a modern API architecture, webhooks are essential. By reversing the communication model from pull to push, they enhance APIs by enabling them to operate asynchronously and in real time. 

This brings several advantages, which can be summarized as follows:

• Efficiency and resource savings: by sending data only when a relevant event occurs, webhooks drastically reduce the number of requests exchanged between applications, resulting in bandwidth savings and reduced CPU usage on both servers;
• Real-time communication: the ability to communicate in real time is crucial for customer-oriented applications (for example: payments, registrations, etc.), which require immediate interactions;
• Notification reliability: webhooks ensure that the system is notified at the exact moment a status changes, a vital feature for events that may take hours or days, such as bank transfer confirmation;
• Simplified architecture: by using webhooks, the receiving application simply needs to expose an endpoint, without managing timers and polling loops, while the sender is responsible for configuring the trigger event.

In essence, webhooks transform APIs from passive data sources into true active notification systems.

Webhooks and polling in API architecture

The fact that webhooks and polling are opposite mechanisms does not mean they cannot be used together. On the contrary, the two models coexist peacefully in thousands of infrastructures and are often used in a complementary way.

Polling, for example, can be used as a “verification pull”, that is, to validate the webhook and ensure the status is confirmed, or to retrieve all the resource data (which may have been omitted from the webhook for security or size reasons).

Webhooks and polling very often coexist within complex asynchronous operations such as video file processing. While the intermediate processing status is updated via polling, the system may provide a completion notification at the end of processing, which instead takes place via a webhook.

The combined use of webhooks and polling makes it possible to maximize efficiency (with real-time push notifications) while maintaining data security and integrity (thanks to targeted pulls).

Especially in complex integrations, the harmonized use of these two mechanisms can prove to be the best strategy to balance immediacy, security, and reliability of processes.