Which HTTP response code indicates a successful API request?

The response code that indicates a successful API request is 200. This code signifies that the request has been successfully processed by the server. When clients receive a 200 response, it typically means that the request was understood and acted upon as intended, often resulting in the requested resource being returned in the response body.

The code 201 indicates that a resource has been successfully created as a result of the request, which is also a successful outcome but is more specific to creation operations, such as when a new entity is added to a database. Thus, while 201 is indeed associated with success, the more general code for success across API interactions is 200.

A 404 code indicates that the requested resource could not be found on the server, meaning the request was unsuccessful. The 500 status represents a server error when the server fails to fulfill a valid request due to an internal malfunction. Hence, these two codes are associated with different forms of failure rather than success.