framework-http-request-headers.md
Comprehensive reference for the eleven HTTP request headers most relevant to server side decisions about how to respond, route, log, throttle, or filter: User-Agent (identity, never to be trusted alone), Accept (content type negotiation), Accept-Language (language negotiation), Accept-Encoding (compression negotiation), Accept-Charset (legacy charset negotiation), From (legacy contact identifier), Host (virtual host selection), If-Modified-Since (conditional GET by date), If-None-Match (conditional GET by ETag), Referer (request origin), and Connection (transport disposition). Built for Bubbles (Debian, Nginx 1.26+, self hosted origin at 169.155.162.118, no Cloudflare or third party CDN in front). Companion to the seven response side frameworks (caching, content, SEO, security, performance, CORS, rate control), UNIVERSAL-RANKING-FRAMEWORK.md, and SEO BUILD REFERENCE v2.4.
This is the first request side framework. The previous seven frameworks documented what the server SENDS in responses. This one documents what crawlers and clients SEND in requests, and how the server reads, validates, and reacts to those headers. The two sides interlock: the server's Last-Modified response is meaningful because clients send If-Modified-Since requests; the server's Vary: Accept-Encoding response only makes sense because clients send Accept-Encoding requests.
