The legal tint limit varies from state to state, county to county. But most states/counties have roughly the same limit. Other than large cities where a lot of illegal activities go on in.
In most places the legal tint level is 35% in the front, and 15% in the back, and you can have nothing on your windshield other than the top 6 inches. However, there is no "tint meter" that a cop can use, most is guessing. I have 15% all around, and have never been stopped for it. Although it is not that dark, and is still somewhat visible up front because of the windshield's light, you can still not make out exactly what is going on in the car, which I like.... And at night, you can not see through it, unless you put your hands on the glass, in which case, I would be forced to open the door and harm you to the fullest extent of my Nine...