HTTP Header Analyzer - HTTP Header Analyzer is an open-source browser extension that allows you to see and analyze the current HTTP request and response header from the website URL.
HttpWatch - HttpWatch: The ultimate HTTP Sniffer for Chrome, IE and iOS
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.
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.
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!