Understand the HTTP request-response cycle

One exchange has two messages

An HTTP exchange begins when a client sends a request. The server processes that request and sends a response. Intermediaries such as proxies or caches can take part, but each hop still observes request and response messages with defined semantics.

GET /guides/cache-validation HTTP/1.1
Host: httpclarity.com
Accept: text/html

Expected result: the request identifies the GET method, a target path, and the representation formats the client can accept. It does not contain a response status.

HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
Content-Length: 1234

Expected result: the response reports an outcome with status 200 and describes the enclosed representation with response fields.

Observe before you explain

Developer tools can show the messages visible to that browser. A command-line client can show a different path through caches, proxies, DNS, or TLS. Record the actual request and response first, then identify which layer could have produced the observation.

Keep the direction explicit

• Methods and request targets belong to requests.
• Status codes belong to responses.
• Fields can appear in requests, responses, or both depending on their defined semantics.
• A browser policy can prevent page JavaScript from reading a response even when the network exchange succeeded.