To check if Diablo 3 servers are down right now, you can use a free web service. There are online tools like isitdownrightnow.com, IsTheServiceDown.com, DownForEveryoneOrJustMe.com, etc. You can open these websites in a web browser, search for Diablo 3 or Blizzard, and then check if the servers are available or down at the moment. If the servers are down, you will not be able to connect to online servers and play the game.