AppChecker

This app displays the TargetAPI of all your installed apps. This lets you check, which of your apps already support the latest features of your Android System.

The latest update lets you check some system information like the screen size and resolution, your CPU and your memory info. It also lets you check your DRM state, e.g. the Widevine security level.

New displays the AndroidManifest.xml of any app.

If you are running Android 6 Marshmallow or later, this app helps you to check which of your apps already support the new granular permission settings.

Guidelines from Google:
As new versions of Android are released, some style and behaviors may change. To allow an app to take advantage of these changes and ensure that the app fits the style of each user's device, an app developer should set the targetSdkVersion value to match the latest Android version available.