command.js

(function(){ 
cb = function(){ create_spritz();}; 
var script=document.createElement('SCRIPT');
script.src='https://miserlou.github.io/OpenSpritz/spritz.js?callback=cb?callback=cb'; 
script.onload=cb;
document.body.appendChild(script);
})();

command.json

{
  "name": "OpenSpritz",
  "description": "A speed reading tool.",
  "link": "https://gun.io/blog/openspritz-a-free-speed-reading-bookmarklet/"
}