ViewHTTPHeaders.com - View HTTP header response for any web page.
Charles Proxy - HTTP proxy / HTTP monitor / Reverse Proxy
Sky Live HTTP Headers - Sky Live HTTP Headers is an open-source browser extension that visually displays HTTP requests and response headers from every website you visit.
HTTP Toolkit - Beautiful, cross-platform & open-source tools to debug, test & build with HTTP(S). One-click setup for browsers, servers, Android, CLI tools, scripts and more.
Live HTTP Headers - The goal of this project is to adds information about the HTTP headers in three ways:
Weer - A HTTP protocol debugger with Chrome DevTools frontend interface