YouTube offers a setting that plays HD video only when you are on Wi-Fi. Open the YouTube, tap the triple-dot button in the upperright corner and tap Settings. Tap to turn on the toggle switch for Play HD on Wi-Fi only. While you are in settings, scroll down and tap to turn on the toggle switch for Upload over Wi-Fi only if you are a YouTube auteur that regularly uploads videos. The good news with YouTube and your monthly data limit is YouTube doesn’t autoplay videos. The bad news, of course, is it does nothing but play videos, which can quickly run up your data use when you stray from a Wi-Fi signal.