RFC 7231 Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content

PROPOSED STANDARD · June 2014 · R. Fielding, Ed., J. Reschke, Ed.

The Hypertext Transfer Protocol (HTTP) is a stateless application- level protocol for distributed, collaborative, hypertext information systems. This document defines the semantics of HTTP/1.1 messages, as expressed by request methods, request header fields, response status codes, and response header fields, along with the payload of messages (metadata and body content) and mechanisms for content negotiation.

Not ingested in full here — read it on rfc-editor.org.