HTTP Header

Detailed Explanation

HTTP Headers are metadata attached to every HTTP Request and HTTP Response. They tell the server and browser important context about the communication — like who you are, what data format you're using, and what's allowed.

Request Headers (what your app sends):

• Authorization: Bearer eyJhbGc... — Your auth token, proving who you are
• Content-Type: application/json — Tells the server you're sending JSON data
• Origin: http://localhost:5173 — Where the request is coming from (used by CORS)

Response Headers (what the server sends back):

• Content-Type: application/json — The response data is JSON
• Access-Control-Allow-Origin: * — CORS permission (who can read this response)
• Access-Control-Allow-Methods: GET, POST, PUT, DELETE — Allowed HTTP methods

Why headers matter for debugging:

Missing or incorrect headers cause some of the most confusing errors:

• Missing Authorization header → 401 Unauthorized status code
• Missing CORS headers → Browser blocks the response entirely
• Wrong Content-Type → Server can't parse your data

You can inspect headers in the Network Tab: click any request, then look at the Headers tab. When debugging, copy the headers and show them to Claude Code — it can spot missing headers instantly.

Related: HTTP Request, HTTP Response, CORS, Authentication, Token, Network Tab, Status Code, JSON