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.
ViewHTTPHeaders.com - View HTTP header response for any web page.
WebSniffer - WebSniffer is an online tool to outlook HTTP request and response headers.
HTTP Header Live - Displays the HTTP header. Edit it and send it.
HTTP Header Spy - HTTP Header Spy is a browser extension that allows you to inspect the request and response header of any website URL.
HTTP Debugger - Debug HTTP API calls to a back-end and between back-ends. Easy of use, clean UI, and short ramp-up time. Not a proxy, no network issues!