HttpWatch - HttpWatch: The ultimate HTTP Sniffer for Chrome, IE and iOS
ViewHTTPHeaders.com - View HTTP header response for any web page.
Postman - The Collaboration Platform for API Development
HTTP Header Live - Displays the HTTP header. Edit it and send it.
Insomnia REST - The most intuitive cross-platform REST API Client ð´
Firefox Developer Tools - Examine, edit, and debug HTML, CSS, and JavaScript on the desktop and on mobile.