What is HTTP? — HyperText Transfer Protocol Explained

What is HTTP? — HyperText Transfer Protocol Explained

Definition

HTTP (HyperText Transfer Protocol) is the foundation protocol of the World Wide Web. It is an application-layer protocol that defines how messages are formatted and transmitted between web clients (browsers) and servers. HTTP follows a client-server request/response model where the client initiates a request and the server responds with the requested resource or an error.

HTTP was developed by Tim Berners-Lee at CERN in 1989 and has evolved through HTTP/1.0, HTTP/1.1, HTTP/2, and HTTP/3.

The Request/Response Model

Every HTTP interaction consists of a request from the client and a response from the server:

HTTP Request

GET /api/users HTTP/1.1
Host: api.example.com
Accept: application/json
Authorization: Bearer abc123
User-Agent: Mozilla/5.0

HTTP Response

HTTP/1.1 200 OK
Content-Type: application/json
Content-Length: 234
Cache-Control: max-age=3600
Date: Mon, 15 Jun 2026 10:30:00 GMT
 
{"id": 1, "name": "Alice", "email": "alice@example.com"}

Structure Breakdown

HTTP Methods

HTTP methods (also called verbs) indicate the desired action to be performed on a resource:

Idempotent means making the same request multiple times produces the same server state. Safe means the request does not modify server state.

Method Examples

GET    /users          — List users
GET    /users/123      — Get user 123
POST   /users          — Create a new user
PUT    /users/123      — Replace user 123 entirely
PATCH  /users/123      — Update specific fields of user 123
DELETE /users/123      — Delete user 123

HTTP Headers

Headers convey metadata about the request or response:

Request Headers

Response Headers

HTTP Status Codes

Status codes indicate the result of the server's attempt to process the request:

1xx — Informational

2xx — Success

3xx — Redirection

4xx — Client Error

5xx — Server Error

HTTP/1.1 vs HTTP/2 vs HTTP/3

HTTP/2 introduced binary framing, multiplexing, and header compression — significantly improving page load performance without changing application semantics.

HTTP/3 switches from TCP to QUIC (based on UDP), eliminating TCP head-of-line blocking and reducing connection establishment time.

Cookies

Cookies are small pieces of data stored by the browser and sent with every request to the originating server:

Setting a Cookie

HTTP/1.1 200 OK
Set-Cookie: sessionId=abc123; Expires=Wed, 01 Jan 2027 00:00:00 GMT; HttpOnly; Secure; SameSite=Lax
Set-Cookie: theme=dark; Max-Age=31536000; Path=/

Cookie Attributes

Caching

HTTP caching improves performance by reusing previously fetched resources:

Cache-Control Directives

Cache-Control: public, max-age=3600, must-revalidate

ETag Validation

# Request
GET /api/users HTTP/1.1
If-None-Match: "abc123"
 
# Response (if unchanged)
HTTP/1.1 304 Not Modified
ETag: "abc123"

LangStop HTTP & API Tools

• REST API Client — Send HTTP requests and test API endpoints
• URL Encoder — Encode URL parameters and special characters
• URL Decoder — Decode URL-encoded strings
• JWT Encoder — Create and sign JWT tokens