Which protocol is commonly used for web services in RESTful APIs?

The choice of HTTP as the protocol commonly used for web services in RESTful APIs is grounded in the fundamental design principles of REST (Representational State Transfer). RESTful APIs leverage the statelessness of HTTP, which allows clients and servers to communicate efficiently by utilizing standard HTTP methods such as GET, POST, PUT, and DELETE. These methods correspond to operations performed on resources, aligning perfectly with REST's resource-oriented architecture.

HTTP provides the necessary structure for sending requests and receiving responses over the web, making it inherently suitable for creating services that are accessible via standard web protocols. Because almost all web browsers and other internet services are built around HTTP, it ensures broad compatibility and ease of use.

Furthermore, using HTTP allows RESTful services to take advantage of features like caching, which can enhance performance, and it supports a variety of data formats like JSON and XML, making it versatile for different applications. This wide acceptance and functionality confirm HTTP as the go-to protocol for implementing RESTful APIs.