This seems so simple. You should be able to use window cleaner on actual windows, right? Well, not car windows. It turns out window cleaners can damage the protective coating on car windows and cause the glass to become cloudy, scratched, or cracked over time.
This is even more true for tinted windows or windshields treated with a hydrophobic coating. Windex can damage both the tint and the window’s protective layer. Worse, a window cleaner can also leave residue on the windshield's rubber trim. And before you say, well, I can use window cleaner on the outside of my car — don't. It can strip away any wax finish and isn't that great for your paint job, either.
Instead, use a gentle soap or Rain-X Auto Glass Cleaner ($3 from Amazon).