REST API and RESTful API is the implementation of the REST architecture. It is the HTTP interface used for communication between the server and the client (e.g. application or website), which is used to read/write/update or for data deletion using the HTTP protocol. It uses various methods, with the primary ones being: GET, POST, PUT and DELETE. The API request should consist of one HTTP method, header, resource path and content. Most web APIs are built around this interface. It is a very useful tool for testing the API is the Postman application.

Stages of working with API:

• The client creates a query in the form of an appropriate address (endpoint).
• The client sends it with the data request.
• The system receives the client's query, processes it and returns a response.

REST API assumptions:

• Separation of user interface from server operations.
• Stateless (the server does not store information about the client)
• Cacheability (responses from the server must contain information whether the downloaded data is updated frequently or rarely, so it is worth to cache them).
• Downloaded resources with metadata should have enough information to be modified or deleted.
• The returned response should contain information needed, for example, to process the message into something like a JSON object.
• HATEOAS (Hypermedia As The Engine Of Application State) are links to related resources. These make it easier to navigate through the API.
• Endpoints should clearly indicate what resource they relate to.
• Separation of layers, i.e. the separation of individual layers in the code, such as: data access, business logic or view.

Advantages of using REST API:

• universality,
• intuitiveness and ease of use,
• easier infrastructure management on the server and client side.