Which of the following is a constraint of RESTful APIs?

• A. Every response must be encrypted with TLS 1.2.
• B. Statelessness, a uniform interface, resource-based URIs, standard HTTP methods, cacheability, layered system, and optional code on demand.
• C. APIs must be versioned using a numeric prefix.
• D. All operations must be synchronous.

Answer: (B)

RESTful APIs are defined by a specific set of architectural constraints that shape how resources are exposed and interacted with. The idea of statelessness means the server doesn’t hold any client session data between requests; each request carries all the information needed for processing. A uniform interface provides consistency across resources, with resources identified by URIs and operations performed using standard HTTP methods like GET, POST, PUT, PATCH, and DELETE. Resource-based URIs ensure that each resource is addressed by its own address rather than embedding actions in the path. Cacheability is important so responses can be stored and reused when appropriate, improving efficiency. A layered system allows intermediate components such as proxies or gateways to handle concerns like caching, authentication, or logging without the client needing to know. Optional code on demand means the server may deliver executable code to the client to extend functionality, but this is not required.

The other options don’t fit because REST does not mandate encryption via TLS as a defining constraint, nor does it require versioning with a numeric prefix, and it doesn’t prescribe a synchronous-only model.