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Key Takeaway
There are a few differences between APIs, webhooks, and WebSockets. APIs work well in CRUD (create/read/update/delete) operations for quick responses, while webhooks offer real-time updates without polling and enable event-driven interactions. WebSockets are continuous bidirectional communication channels, ideal for real-time applications. Choose APIs for quick, customized interactions, webhooks for instant updates, and WebSockets for continuous two-way communication.
How do you differentiate between application programming interfaces (APIs), webhooks, and WebSockets? Each performs data exchange between web application clients and servers, or between other elements in information systems. They are quite distinct from one another, however, with different architectures and functionalities. Each has its own most suitable use cases.
An API is a software interface between two or more software programs. It is a set of functions and procedures that enable applications to access the features or data of an operating system, application, or other services. While there are a wide variety of APIs, when people talk about APIs today, they are invariably referring to those that transfer data using XML or JSON over the HTTP protocol.
APIs work well for create/read/update/delete (CRUD) functions. For example, a mobile banking application that needs the user’s investment account balance will call on an API offered by the investment firm. For this to work, the API comprises a contract with rules that govern the connection between API consumers and the API.
Webhooks enable event-driven interactions between web-based applications. In contrast to traditional client/server “polling” processes that required a subject system to “ask” an observer system if it has any new data, with a webhook, the observer only sends data to the subject upon a predefined event. This is known as a user-defined HTTP callback. For example, if a user logs in and starts a new session, that event might trigger the observer system to send data to the subject. The process is the opposite of an API’s call/response interaction, leading some to call webhooks “reverse APIs.”
Webhooks get rid of the constant checking involved in polling. They work using static URLs that point to APIs in the subject system. Webhooks are completely Internet-based, so all communications take place over HTTP. This setup cuts down on the application’s load, as HTTP calls only take place when there is a relevant event. For these reasons, webhooks work well for situations where a web app has to call on its back end.
WebSockets are real-time, persistent, and bidirectional communication channels based on the WebSocket protocol. The full duplex channel runs on a single TCP connection. WebSocket protocol is different from HTTP, though both operate at layer 7 of the standard OSI network stack. It enables a web browser, or comparable client, to interact with a web server. Like webhooks, WebSockets do not need the API’s request/response process to execute an interaction between the client and server.
With a WebSocket, messages pass back and forth on an open connection. This setup allows service providers to send messages to users any time they need to. The most popular browsers support WebSocket protocol, including Firefox, Microsoft Edge, Safari, and Google Chrome. Based on this level of support, WebSockets are great for real-time web applications.
APIs, Webhooks, and WebSockets each have a favored type of use case. APIs, for example, with their request/response mode of interaction between client and server, are well suited to applications that need quick responses from back-end operations. The difficulty is that APIs do not provide a way for the server to communicate with the client without a request.
For example, if an API requests that the server perform a task that takes time, the API will need to check—or “poll”—the server periodically for updates on the status of the task. This is not efficient. A Webhook or WebSocket could perform this operation better than an API.
Webhooks are a preferred choice over APIs in systems where nearly real-time data updates are required. When an API is in polling mode, which means it is asking for updates on a set time interval, it will be sluggish in comparison with a real-time webhook interaction. A webhook, as noted above, instantly pushes the update to the client as soon as a triggering event has occurred.
APIs are better than webhooks when customization is necessary. This might be the case in a system with highly variable data, such as Internet-of-Things (IoT) environments. Here, using customized API polling works better than a webhook because the probability of an API generating an actionable response is high. Additionally, APIs have an advantage over webhooks in situations where a webhook’s push of data gets ignored because the client endpoints are offline. Webhooks do not have a built-in way to deal with this potentiality.
Webhooks do well when a web app needs to keep track of changes in an external service, e.g., new account transactions. Because webhooks are stateless, they don’t require an open connection. This makes them easier to scale than WebSockets. They can handle more subscribers. Being stateless also means that webhooks are a bit simpler to manage.
WebSockets, in contrast, are best for situations where there has to be two-way communication between the client and server in real time. The simultaneous editing of a web document by multiple people is a good example of this capability. For each user editing the document, his or her browser would be connected to the server containing the document through a WebSocket. If one user makes an edit, the change goes from his browser client to the server before the second user sees it. The WebSocket relays the changes in real time.
Communication between client and server is essential in a web application. APIs, webhooks, and WebSockets perform this function. Each does it in its own distinct way, however. APIs are good for data request/response interactions where customization is needed. Webhooks are best suited to use cases that require event-based information exchange, while WebSockets are ideal for applications that need a continuous, two-way communication channel. As developers consider their needs for a particular aspect of web application communication, they should be able to find the right solution among these three choices.
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Harold Bell
Harold Bell was the Director of Content Marketing at Noname Security. He has over a decade of experience in the IT industry with leading organizations such as Cisco, Nutanix, and Rubrik, and has been featured as an executive ghostwriter in Forbes Technology Council and Hacker News.
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