WebSniffer is an intelligence platform in the making that is going to track changes on the web and provide actionable insights to its users. The online tool can currently view HTTP response headers of any web page, do domain name, IP address lookups and provides user’s browser information such as IP address, user agent and more.
Charles Proxy - HTTP proxy / HTTP monitor / Reverse Proxy
Modify Header Value (HTTP Headers) - Modify Header Value (HTTP Headers) is a browser extension that allows you to add, modify or remove a header for any request to your preferred domains.
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.
HTTP-Repeater (HTTP/s Live Headers) (Beta) - HTTP-Repeater (HTTP/s Live Headers) (Beta) is a browser extension that lets you capture browser requests and repeat the process in a loop automatically.
Weer - A HTTP protocol debugger with Chrome DevTools frontend interface
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.