Are REST APIs synchronous or asynchronous?

REST (Representational State Transfer) APIs are primarily synchronous. When a client makes a request to a RESTful web service, it waits for the server to respond before performing other actions. This synchronous operation aligns with REST’s stateless nature, where each request from the client to the server must contain all the information the server needs to understand and respond to the request.

However, it’s important to note that REST APIs can be used in an asynchronous manner as well. This is typically managed by the client’s architecture rather than the API itself—for example, by using asynchronous JavaScript (AJAX) on the web client side to handle REST API requests without blocking the user interface. In such cases, the client doesn’t wait for the response immediately but sets up a callback mechanism to handle the response once it arrives, allowing the client application to continue other processes in the meantime.

Thus, while REST APIs are designed to operate synchronously, they are versatile and can be adapted to function asynchronously depending on the needs of the application and its design.