HTTP header wizard

Pick the right header for a use case (caching, CORS, auth, conditional requests, content negotiation), look up what any header means and what its real-world gotchas are, or compare two headers side by side. The whole site runs in your browser — no backend, no tracking, no cookies.

Modes

Picker — "I need to control caching" / "I need to set up CORS" / "I need to authenticate" walks you through which headers actually matter and which ones are leftover noise.
Lookup — search or browse any header. See its purpose, syntax, common values, the spec, and the real-world gotchas (e.g. Cache-Control: no-cache does not mean "don't cache").
Compare — pick any two headers for a side-by-side view. Useful pairs: Cache-Control vs Expires, ETag vs Last-Modified, X-Forwarded-For vs Forwarded.

Heads up: the interactive Picker, Lookup, and Compare modes need JavaScript. Per-header reference pages live at predictable URLs like /h/cache-control if you'd like to read directly.