REST APIs and HTTP APIs are terms often used in web development and system integration. Let's clarify what they mean and how they differ:

REST APIs

REST, standing for Representational State Transfer, is an architectural style for designing networked applications. RESTful APIs are APIs that adhere to the principles and constraints of REST.

Key Features of REST APIs

1. Stateless: Each request from client to server must contain all the information needed to understand and process the request. The server doesn't store any session state.
2. Client-Server Architecture: The client and the server operate independently, and the client doesn't need to know the inner workings of the server.
3. Uniform Interface: REST APIs have a uniform interface, which makes them easier to understand and use.
4. Cacheable: Responses must define themselves as cacheable or not, to prevent clients from reusing stale data.
5. Layered System: REST allows for a layered system architecture where client-server interactions can be mediated by intermediate layers.

Common Operations

• GET: Retrieve a resource.
• POST: Create a new resource.
• PUT: Update an existing resource.
• DELETE: Remove a resource.

HTTP APIs

HTTP (Hypertext Transfer Protocol) is the foundation of data communication on the World Wide Web. An HTTP API is a server-side API that uses HTTP requests and responses.

Characteristics

1. Protocol Specific: HTTP APIs are tied to the HTTP protocol.
2. Versatile: They can be used for various styles of web services, not just REST.
3. Flexible: HTTP APIs may not strictly adhere to REST constraints and can be designed in various ways to meet specific needs.

HTTP API vs REST API

• REST API is a Subset: All RESTful APIs are HTTP APIs, but not all HTTP APIs are RESTful. REST is a set of guidelines (or architectural style) for building APIs, and it utilizes HTTP for communication.
• Design Philosophy: RESTful APIs strictly follow REST principles, like statelessness and a uniform interface. HTTP APIs might not adhere to these principles.
• Use Cases: RESTful APIs are well-suited for web services requiring scalable and flexible architectures, like public web services. HTTP APIs are used when you need more flexibility in how you handle requests and responses.

Conclusion

In practice, the term "HTTP API" often refers to APIs that use HTTP for transport but don't strictly adhere to all the REST constraints. Meanwhile, a "REST API" specifically adheres to the REST architectural style, making it a type of HTTP API with more defined constraints and principles.

Whether to use REST API principles or a more flexible HTTP approach depends on the specific needs of the application and the desired properties of the API, such as scalability, statelessness, and the need for a uniform interface.

Reference:

• 8 REST API Interview Questions Every Developer Should Know
• A Guide to Understanding RESTful API in System Design Interviews
• REST vs GraphQL vs gRPC