HTTP Headers

Metadata controlling Caching, Authentication, Compression, content negotiation, session state, security policy, and connection behavior flows through HTTP headers, name-value pairs exchanged between clients, servers, and intermediaries during every request-response cycle.

Table of Contents

Usage

Headers appear in both requests and responses. Request headers describe client preferences and context. Response headers convey server decisions and instructions. Representation headers describe the message body (encoding, language, and length). Transfer-related headers like Transfer-Encoding and Content-Length describe the message content framing.

End-to-end headers travel the full path from client to server (or server to client) and are preserved by intermediaries. Hop-by-hop headers apply only to the connection between adjacent nodes and are not forwarded.

Modern headers use structured fields, a common type system of integers, strings, tokens, lists, dictionaries, and parameters with strict parsing rules.

HTTP header categories and names

Authentication

Caching

Client hints

User-Agent client hints

Preference client hints

Conditionals

Connection management

Content negotiation

Controls

Cookies

CORS

Content information

Content digests

Dictionary compression

Fetch metadata

HTTP signatures

Preferences

Priority

Proxies

Range requests

Rate limiting

Redirects

Reporting

Request context

Response context

Security

Privacy

DPoP

Speculation

Transfer coding

Tracing

WebSocket

Web linking

ACME

Deprecated or experimental

Other

AWS

Akamai

Cloudflare

Caching (vendor)

Load balancer and infrastructure

Microsoft / ASP.NET

Next.js / Vercel

Netlify

LiteSpeed

Drupal

Shopify

Wix

GitHub

Facebook

Fastly

Security (vendor)

See also

Last updated: April 4, 2026