Show page headers.

showHeaders.js

// showheaders.js
// https://github.com/bgrins/devtools-snippets
// Print out response headers for current URL.

(function() {

  var request=new XMLHttpRequest();
  request.open('HEAD',window.location,true);
  
  request.onload = request.onerror = function () {
    var headers = request.getAllResponseHeaders();
    var tab = headers.split("\n").map(function(h) {
      return { "Key": h.split(": ")[0], "Value": h.split(": ")[1] }
    }).filter(function(h) { return h.Value !== undefined; });

    console.group("Request Headers");
    console.log(headers);
    console.table(tab);
    console.groupEnd("Request Headers");
  };
  
  request.send(null);

})();