Which class of HTTP response status codes signifies successful client requests in a RESTful web service?

The class of HTTP response status codes that signifies successful client requests in a RESTful web service is the one that begins with the number 2. Specifically, these codes indicate that the client's request was successfully received, understood, and accepted by the server. Examples of status codes in this range include 200 (OK), which indicates a successful request, and 201 (Created), which confirms that a resource was successfully created due to a request.

This distinction is critical for developers working with APIs, as it signals the outcomes of interactions, helping in debugging and managing responses from a web service effectively. The other classes mentioned serve different purposes; for instance, 1xx codes are informational responses, 3xx codes are used for redirection, and 4xx codes indicate client-side errors. Understanding these classifications helps in better handling various types of responses in API development and integration.