In order to find out if it’s a legal driveway, you can look at city databases to see if the curb cut — the area of the sidewalk that slopes down to street level — was installed with a permit. The Department of Buildings maintains records on DOB Now and the Building Information System. However, this record search can be complicated, especially for curb cuts that have been there for decades. You can also call 311 and say that you suspect it’s illegal, and an inspection will give you an answer.