Webhook vs. API: Which mechanism is better?

What is a webhook?

A webhook is a mechanism that allows one application or service to push data to another. Webhooks are a type of event-driven communication medium, meaning that a certain kind of event triggers the movement of data from a source to an endpoint.

Webhooks typically use the HTTP protocol to transport data. In this sense, webhooks are like any other HTTP request that a web application might make. However, webhooks are a special type of HTTP request because their main purpose is to push data using an event-driven architecture. Webhooks are not particularly useful for tasks like serving content to a website, which other types of HTTP requests can manage.

What is an API?

An application programming interface, or API, is a mechanism that allows applications or services to communicate with each other. Generally, APIs work by enabling a client to submit a request for information to an API server. The server then responds with the requested data. The request and response data require proper formatting to conform with the API design and ensure the client and server can interpret the data.

APIs can exchange data using a variety of protocols. HTTP is one, but because HTTP supports limited types of data and data formatting, developers often use protocols specifically designed for APIs, like SOAP.

Webhook vs. API: Key similarities

At a functional level, webhooks and APIs serve similar purposes, and there is some overlap between the use cases they can support. Webhooks and APIs are alike in that both do the following:

• Make it possible to move data between applications or services in real time.
• Implement event-driven communication. This is the main purpose of webhooks, but APIs can support event-driven data movement alongside other use cases.
• Require developers to format and structure data in a way that both the producer and the recipient of data can interpret.
• Facilitate the movement of data using the HTTP protocol. However, in the case of APIs, this is just one of several protocol options available.

Webhook vs. API: Key differences

APIs can perform many of the same tasks as webhooks, but APIs have capabilities that webhooks don't support. The following categories detail the main differences between the two technologies.

Data movement model

Webhooks push data, whereas APIs allow a client to pull data from a server.

This difference in functionality makes webhooks ideal for use cases where data needs to move in just one direction, like sending notifications whenever a certain type of event occurs. But if an application or service needs to pull data upon request, an API is required.

Data streaming

Webhooks allow for the periodic movement of data, but APIs typically keep communication channels between clients and servers open, enabling the exchange of repeated messages. For this reason, APIs are better than webhooks for use cases that involve real-time data streams.

Security

Without customization, a basic webhook can't format or inspect the data it pushes. As a result, it cannot enforce security policies, unlike an API server that could remove sensitive data before sending it to a client.

Webhooks often require an open, publicly accessible HTTP endpoint for other applications or services to send data. This potential vulnerability might allow malicious actors to carry out attacks like flooding the endpoint with bogus requests in an attempt to cause it to crash. In contrast, APIs can require authentication before clients are allowed to interact with servers.

There are ways to thoughtfully implement and maintain webhook security, but APIs are generally a more secure option for handling sensitive data and managing risk.

Complexity

An API must provide a way for a client to request data and for a server to respond to the request. APIs can also support other features, such as data inspection and transformation, as part of the request-response process. Implementing these capabilities requires a fair amount of effort on the part of developers.

By contrast, webhooks are simpler to build because they only require logic for pushing data from a source to a destination.

Cost

When compared to webhooks, API complexity often translates to higher operating costs, hosting costs and egress costs. For example, APIs consume more memory and CPU resources to support complex communications. The repeated exchange of messages also increases the amount of data moving across the network.

When to use a webhook vs. API

In general, webhooks are better than APIs when the following criteria are met:

• Data needs to move in just one direction.
• Data delivery happens periodically rather than over streams.
• No data processing is required during the communications process. The data moves from a source to a destination.

Webhooks work well for building notification systems. They are also useful for creating automated workflows where one action, like committing source code to a server, should trigger another action, like compiling the code.

In most other situations involving movement between applications or services, APIs are better. APIs provide more control over how data moves, make it easier to keep communication channels open and provide security capabilities that webhooks lack.

Chris Tozzi is a freelance writer, research adviser, and professor of IT and society. He has previously worked as a journalist and Linux systems administrator.