Request and Response Headers

Request headers you will see

• Content-Type — body format you are sending
• Accept — formats you can handle
• Authorization — credentials
• User-Agent — client identity

Response headers that help

• Content-Type
• Location after creates
• Cache-Control for cacheable GETs
• ETag / Last-Modified for conditional requests

Example exchange

A POST with JSON and an auth header.

POST /api/books HTTP/1.1
Host: api.example.com
Authorization: Bearer TOKEN
Content-Type: application/json

{"title":"Practical APIs"}

Custom headers

Prefix carefully (often X- is legacy). Prefer standard headers when they exist. Use correlation IDs for tracing across services.