Press F12 while playing game to open the console window. Enter one of the following codes and then press ENTER.

Code - Effect

byzantine - All diplomacy is success
nofog - Remove fog of war
showid - Show country ID
die - Kill selected character
norevolts - Population won't revolt
gold - +1000 gold
piety - +1000 piety
prestige - +1000 prestige
nowar - AI won't declare war