API, WebSocket, or WebHook: what’s the difference and which one to choose

Every day, millions of systems exchange information with each other. While the processes may look the same from the outside, the way data is transmitted internally varies.

These methods differ in request mechanics and other criteria. Some of the most popular approaches include API, WebSocket, and WebHook. These well-known mechanisms are used to connect internal and external systems.

In this article, we will explore what API, WebSocket, and WebHook are, how they differ, where they are used, and which method to choose for development.

API: What it is and where it’s used

API is an application programming interface that acts as an intermediary between services interacting with each other. It can be loosely referred to as a "contract" that specifies what information can be entered, what can be retrieved, and what actions can be performed. The application programming interface regulates data transmission and ensures its integrity on both sides.

How API works

Service #1 wants to retrieve information from Service #2. To do this, it calls Service #2’s API to specify the actions that need to be performed. Service #2 also sends data not directly, but through the API interface. This way, Service #1 doesn’t need to delve into the internal processes of Service #2’s program to obtain the necessary information.

APIs are classified into open and closed. Open APIs are intended for use by third-party developers. They are used when creating services that will exchange data with a program providing a public API. In other words, developers leverage existing solutions for their projects. Closed APIs are used for internal tools within companies, and access to them is restricted for third-party developers.

Where API is used

Many services and applications that are needed by users in business and daily life operate via API. Online maps, which integrate data on road congestion and traffic movement, flight booking aggregators, calendars for scheduling meetings and appointments with specialists — these tools work with APIs. This technology is also used for conducting transactions and simplifying registration across multiple services using data from an existing account. For example, one can log in to an online store using a Google account or to an educational platform using VK ID. There’s no need to create a new password; simply confirm the login through the existing account.

WebSocket: what it is and where it is used

WebSocket is a technology that provides two-way, continuous real-time data transfer between the client (user) and the server. It allows for fast and seamless information exchange without delays, eliminating the need to refresh the page to display new data. WebSocket uses HTTP only during the connection setup phase, after which it switches to its own protocol that ensures two-way communication.

How WebSocket works

With WebSocket, the user can send requests and receive quick responses from the server. Moreover, when information on the server is updated, it is automatically sent to the user, even if they did not initiate the request. This is possible because of the continuous data transfer channel, which is established through a single initial connection and remains open without needing to restart. A restart of the channel is only required if a WebSocket error occurs.

Where WebSocket is used

The WebSocket technology is essential for online services where interactive and rapid communication is important. It is widely used in online games, where constant real-time data exchange is required. WebSocket is also applied in social networks for sending push notifications, such as notifying users of their order status when it is updated.

This technology is also utilized in messaging apps, where instant message delivery is critical. WebSocket facilitates fast data updates on trading platforms, where exchange rates and quotations change in real-time. Furthermore, the protocol is indispensable in collaborative applications, such as interactive whiteboards, where user actions need to be synchronized in real-time.

Webhook: what it is and where it is used

A webhook is a way for a system to quickly respond to user actions. To put it simply, a webhook is a mechanism that sends a notification or data when a specific trigger occurs.

How Webhook works

To understand how a webhook works, let's break down how to create one. First, a user address is formed, where messages from the server will be sent. Then, the actions that will trigger the webhook are defined. When an event (such as a client request) occurs, a notification is sent to that address.

For example, when a person places an order on a website — this is the trigger that activates the webhook. A response is sent to the action: a payment link is sent via SMS.

Where webhook is used

This method is used in marketing and sales to quickly interact with customers. Primarily, it is used for notifications about various events: an order placed, a new comment, a request, a status update, a like, a repost, and more. Webhook is also used for marketing automation and personalizing offers. Information can be sent through a webhook to platforms like bots, SMS, email, push notifications, and more.

The technology also optimizes internal data processing within a company. Triggers can include events like order reception in a store, system failures, the start and end of a process, and so on.

API, WebSocket, and WebHook: What’s the Difference

These mechanisms serve as communication methods between different services and applications. They mainly differ in how the request is executed. Additionally, the type of communication varies: it can be either one-way or two-way. The differences are clearly shown in the table.

API, WebSocket, and WebHook: what to choose

The choice of technology depends on technical capabilities and the functions that need to be performed. Limitations of the methods should also be considered, as they can become a decisive factor.

API

Useful when you need to use data from a third-party application to develop your own. It is suitable for systems that quickly respond to requests. API is a flexible interface with extensive functionality, relatively simple, and does not require complex configurations. When working with an API, ready-made tools are used, which significantly simplifies development and reduces costs.

A drawback of the interface is the inability of the server to reconnect with the browser if needed. Additionally, not all services provide open APIs.

WebSocket

A mechanism best suited for services that require continuous real-time communication. The protocol is compatible with most resources and works equally well with websites and mobile applications.

However, in terms of speed, this option is more suitable for web-based solutions than for applications, as it requires significant resources. Additionally, it is difficult to scale.

WebHook

Used in cases where a quick response to user actions is required, while resource consumption needs to be minimal. Server load is reduced since data is transmitted only at the moment of an event. This solution is quite versatile, easily scalable, but requires initial configuration. Webhooks are particularly useful for services utilizing marketing campaigns.

Summary

Various methods exist for exchanging information between online services. API acts as a kind of contract that defines the rules for data transmission. This interface can be open to third-party developers, allowing them to use ready-made solutions. API is used when quick responses to requests are needed and when simplifying the development process is a priority.

WebSocket is a method of bidirectional data transfer, used in services where interactive real-time communication is essential.

Another approach, WebHook, works by sending notifications in response to a predefined trigger. It is most commonly used for marketing campaigns and other types of alerts.

The choice of data exchange method depends on the type of services and business needs, including speed, reliability, and cost.