A REST API is an application programming interface that follows the principles of REST (Representational State Transfer), an architectural style for designing web services¹. A REST API allows clients to access and manipulate resources on a server using HTTP methods such as GET, POST, PUT, PATCH, and DELETE².

Some of the main characteristics of a REST API are:

• Uniform interface: The API requests and responses should use a consistent format and structure, such as JSON or XML. The API should also use a standard naming convention for the resources and their attributes, such as nouns in plural form¹.

• Client-server decoupling: The client and the server should be independent of each other, meaning that the client does not need to know the details of the server implementation, and the server does not need to know the details of the client application. The communication between them should be based on the URI (Uniform Resource Identifier) of the resources and the HTTP methods¹.

• Statelessness: The API should not store any information about the client state on the server. Each request should contain all the information necessary to process it, such as authentication tokens, query parameters, or request body. This makes the API more scalable, reliable, and secure¹.

• Cacheability: The API responses should indicate whether they can be cached by the client or not, using HTTP headers such as Cache-Control or ETag. This can improve the performance and efficiency of the API by reducing the network traffic and server load¹.

• Layered system: The API should be composed of multiple layers of components, such as load balancers, proxies, firewalls, or gateways. Each layer should only know about the adjacent layer, and not about the whole system. This can enhance the security, modularity, and scalability of the API¹.

• Code on demand (optional): The API can optionally provide executable code to the client, such as JavaScript or Java applets, to extend its functionality or improve its user interface. This can make the API more dynamic and adaptable to different contexts¹.