ViewHTTPHeaders.com - View HTTP header response for any web page.
Fiddler - Fiddler is a debugging program for websites.
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.
Proxyman.io - Proxyman is a high-performance macOS app, which enables developers to view HTTP/HTTPS requests from apps and domains.
Live HTTP Headers - The goal of this project is to adds information about the HTTP headers in three ways:
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.