This app is no longer recommended by us, instead we suggest you to use Glasswire.
Bytes insight, displays real time per app data usage statistics as a notification that updates itself.It is available for free in the play store.The installation procedure is as simple as downloading the app and turning global switch on..! The app displays the data usage of an app along with its name.You can reset the counter anytime from within the notification. On Android 4.1+, a list of recent traffic consuming apps is included in the expanded notification.The app itself weighs a mere 128kb in terms of size. It helps you deduce whether the connection speed is slow because of any apps downloading something in the background or whether your data provider is limiting it.