The promise between programs is written in a language, and the language is smaller than you fear: an address with four rooms, a request with three parts, a response that mirrors it, five verbs with real meanings, and a three-digit verdict you can read at a glance. Five topics of pure reading fluency — complete, real messages, every character of them plain text — so that when you start sending your own in Chapter 3, nothing that comes back will look foreign.
Chapter 1 established what an API is: a written promise between programs. This chapter teaches the language the promise is written in. HTTP — the set of rules for how requests and responses are put into text — sounds like the moment a beginner's book turns technical. It is actually the moment everything becomes concrete, because HTTP is short, regular, and readable, and by the end of five topics you will have read complete, real messages in it.
The route: the URL taken apart into its four rooms. The request — verb, envelope notes, and sometimes a parcel. The response — verdict, notes, answer. The five verbs and the one distinction among them that will someday save you a double booking. And the three-digit verdicts, read at a glance by their first digit. Nothing here is sent yet; this chapter is pure reading fluency. The sending starts immediately in Chapter 3.
Two plain-text messages — the whole language
The request
Method + address + headers + (sometimes) a body. Four readable lines.
The response
Status + headers + (usually) a body. The mirror image, wearing the same suit.