HTTP Explained: Requests, Responses and Headers
HTTP is an application protocol for requests and responses. A client asks for a resource or action; a server returns a status, headers and sometimes response content.
Published by Protocol Explorer · Reviewed
An HTTP request
A request identifies a method such as GET or POST and a target resource. Header fields carry context such as the accepted content types or authentication information. Some requests also include content.
An HTTP response
The response includes a status code and header fields, and may contain content. For example, 200 indicates a successful request, 404 indicates that the server did not find a current representation, and 500 indicates a server error.
HTTP and transport
HTTP describes application semantics. HTTP/1.1 commonly runs over a TCP connection; HTTPS adds TLS protection. HTTP/2 and HTTP/3 use different framing and connection arrangements while retaining HTTP semantics.
Read an exchange
Identify the method and target first, then match the response status to the request. Inspect content type, caching and length-related headers where present. Headers and content have different roles and should be interpreted separately.
Follow an example step by step
- Start with the client request and identify its method, target and Host or authority.
- Match the response status to the request; inspect content type and any caching fields.
- Follow a second request to see whether the connection is reused; HTTP semantics and wire framing are separate.
Common interpretation mistake
A 404 is an HTTP response, so it proves an HTTP server or intermediary replied; it does not by itself identify why the resource is missing.
Key point to remember
HTTP is stateless at the protocol level; applications can maintain state with mechanisms such as cookies.
Try the interactive lesson
Open Protocol Explorer and select HTTP to follow the exchange packet by packet. The HTTP lesson is free and does not require an account. Pro is a one-time $4.99 purchase for the full library; an account is required to buy and restore it.
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Primary reference
Related protocol lessons
TCP · UDP · HTTPS · How to read a packet