Webhooks vs APIs: What's the difference?

Whether facilitating real-time interactions on social media or sending notifications about recent transactions, applications must provide their services as quickly as possible to keep their users satisfied. This is especially necessary in contexts where applications rely on other applications to provide all of their functionality.

There are two primary ways that apps communicate with each other: webhooks and application programming interfaces (API). These technologies occupy some common ground but are not interchangeable, and provide different base functionalities for different purposes. Therefore, the question of “webhook vs. API” typically boils down to the type of communication that your app requires.

In this post, we’ll take an in-depth look at the similarities and key differences between webhooks and APIs, and their potential use cases. By the end, you’ll be able to determine when it’s most appropriate to use each tool.

Understanding the difference between webhooks and APIs

Both webhooks and APIs are communication tools in the sense that we use them to send lightweight data between software applications — but there’s more to their functionality than that. Let’s take a closer look.

What’s a webhook?

A webhook is an event-based service that enables one application — the source application — to send real time data to another — the client or target application — when a specific event occurs. That data transfer, which is initiated by an HTTP (or HTTPS) request, is unidirectional and takes place in real time. 

Webhooks work in three steps. First, the developer defines the trigger event, typically a specific change in the state of a dataset. Then, the webhook “listens” for that event.

Finally, when the event happens, the source application makes an HTTP request (often containing JSON) to the callback URL which is defined in the target application. The callback URL is an API endpoint containing the logic that executes in response to the event.

Below is a typical webhook request flow chart:

Webhook use cases

Webhooks function to prevent a target application from having to repeatedly ask or poll for data. Instead, the target application receives automatic, one-way data updates from the source application when the predefined trigger occurs. This design approach has made webhooks essential in systems like news apps and ecommerce sites that value speed and must send and receive data in real time. 

One potential use case for a webhook is a static website that must be rebuilt each time data changes in its CMS — perhaps when a customer updates their address or their subscription tier. In this example, you could define and configure a webhook that listens for the relevant CMS update and then sends an HTTP request to the designated endpoint to trigger a build with that real time data. This approach ensures that the site always stays up to date.

Webhooks might be useful if you need to: 

• Receive Slack notifications about important work events, such as build failures, potential cyber attacks, or anything related to critical workflows.

• Send data about unusual financial activity to a bank, or notify a customer about a charge to their account.

• Send scheduled reminders about upcoming meetings and events to departments, teams, or individual colleagues.

• Send real-time notifications to airline passengers about a change to a scheduled flight time.

• Send notifications about price changes, discounts, or flash sales.  

• Send an automated email to a user following an online form submission.

Since webhooks only facilitate data transfers in one direction, the client or target app cannot send data back to the source application. If you’d like to know more, check out our ultimate guide to Contentful webhooks for details on how they function in a composable content platform.

What’s an API?

An application programming interface is a digital communication layer that facilitates exchanges of data between internal or external applications. There are several types of API, many of which incorporate acronyms into their name — so, you’ll often hear references to GraphQL, SOAP API, or REST API. 

While a webhook only sends data once in response to a trigger event, APIs maintain robust, ongoing communication between applications, with API calls generating a data “conversation” made up of requests and responses between API endpoints. Not all APIs are classifiable as “web API” because they may only send and request data within a computer operating system between local programs and routines, rather than to and from an external system.

The first step in the API communication process is a client application sending an HTTP request to a web server, according to predetermined specifications. Then, depending on the type of request and included parameters, the server responds by sending back meaningful data to the client.

For example, imagine a user checking the weather on their smartphone. The phone’s weather app makes an HTTP GET request to a remote API server, which then sends the relevant data back. The phone then populates this data in the app for the user to view.

API use cases

From different branches of a global bank or news agency to take-away food brands and drivers navigating with Google Maps, APIs are the most popular method for connecting and exchanging information between different software systems. 

Developers use APIs when their programs require two-way communication, with a client application sending a request to a web server and the server returning a response. The universal nature of APIs makes them the cornerstone of modern web interactions and, as such, you can find them in just about every industry. 

Furthermore, the flexibility of APIs enables applications to share data or complex functions with one another (the Android and iOS versions of a weather app using the same API, for example) so each app can accomplish more without additional feature programming. 

An API might be optimal if you need to: 

• Share data between websites and social media platforms.

• Find and retrieve media, and make user recommendations on a streaming platform.

• Handle transactions between an ecommerce site and a customer’s bank. 

• Find and display information about shops or locations on a virtual map. 

• Search for a suitable vendor on a crowd-sourced service-provider platform.

Webhooks and APIs: Choose the right tools

APIs remain the predominant choice for web interactions in which data is being constantly updated since they allow flexible communication in a machine-readable format, regardless of differences between the client and source applications.

That’s not to say that the API could or should replace webhooks entirely — in fact, webhooks may be characterized as a more lightweight subset of API. It might help to think of an API as a highly capable personal assistant that can tailor its services to the changing needs of a user, and a webhook as a highly efficient news delivery assistant that brings you the headlines as soon as the story you’re interested in breaks.

Both webhooks and APIs are essential to the functionality of modern applications — so much so that choosing the right one may require a bit of debate. If you’re about to kick that process off, consider the following factors: 

• Communication: APIs are optimal when you need to create, read, update, and delete data (CRUD) because webhooks lack any capability to manipulate information. On the other hand, if you merely need a notification when certain events occur, webhooks make the most sense.

• Resources: Because they only work in one direction and handle a limited amount of information, webhooks tend to be less resource-intensive than APIs that must constantly poll for new data.

• Latency: Both APIs and webhooks are good at sending data quickly, but it's worth noting that, because they're optimized around low latency, webhooks provide a potential advantage if speed or real-time data is a deal-breaker.

• Security: APIs can carry out more complex data transfer tasks than webhooks and typically support more robust security measures — providing those measures are designed and applied effectively. 

Webhooks vs. API: The verdict

All things being equal, the deciding factor in a choice between using webhooks or APIs should be the frequency with which the data in your app needs to be updated. For more frequent updates, choose an API. For less frequent, and more specific, updates, go for a webhook. 

With that said, framing the issue as “webhook vs. API” doesn’t necessarily capture the nuance. Both APIs and webhooks are part of the fabric of the web, and both ensure that applications we use every day continue to perform at the level we expect. 

Regardless of your choice or your level of knowledge about APIs and webhooks, rest assured that Contentful speaks both! Sign up for a free Contentful account and see how our market-leading Contentful Composable Content Platform can support your project or business.

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