HTTP is an application protocol for exchanging requests and responses between clients and servers. It is the central protocol used to transfer web resources and to build many web APIs.

Requests

An HTTP request contains a method, a target resource and headers, and may contain a body.

Common methods include:

• GET to retrieve a representation;
• POST to submit data or request processing;
• PUT and PATCH to modify resources under appropriate application semantics;
• DELETE to request removal.

Responses

The server replies with a status code, headers and optionally a body.

Examples include:

200 OK
404 Not Found
500 Internal Server Error

The status code describes the result of the HTTP request, not whether every application-level goal was semantically successful.

Headers and bodies

Headers carry metadata such as content type, caching information or authentication data. The body can contain HTML, JSON, an image or any other media type understood by the participants.

Stateless protocol semantics

Each HTTP request is independently meaningful at the protocol level. Applications can still build sessions by sending identifiers such as cookies across several requests.

HTTP and HTTPS

HTTPS is HTTP carried through a security layer that provides encrypted and authenticated communication with the server under the relevant certificate and trust model.

HTTP defines the web request-response semantics; lower transport and security layers carry those messages between endpoints.