Which HTTP response code signifies a successful API request?

The response code that signifies a successful API request is 200. This code indicates that the request has been successfully processed by the server, and the response typically includes the requested content.

A 200 status code is a fundamental part of HTTP, representing a standard success response, making it essential for developers to recognize it as an indication that the operation completed without issues.

The other options have different meanings: 400 indicates a bad request due to client error, while 404 signals that the requested resource could not be found on the server. The code 201, although also a success response, specifically indicates that a new resource has been successfully created as a result of the request, such as when a new user is registered or a new item is added. Thus, while 201 is indeed a successful response, 200 is the more general code for successful requests.