A super useful reference guide to using NSDateFormatter format strings. NSDateFormatter.com lets you test out format strings by entering a date, format string and locale. The output of NSDateFormatter is immediately displayed along with several common examples ready to copy and paste into Xcode. The website is written with Swift 3 so actually uses NSDateFormatter under the hood to guarantee accuracy in the way it parses dates. There's also a handy reference that describes what each format string character means.