How do you test whether an object is level with the surface? There are lots of free apps known as Bubble Level on Android which do the job, but thanks to the Google's new feature, you just need to do as follows to bring the Bubble Level on Android without installing any 3rd part app:
1. Open the Google Now or Google Search or Google Chrome on your Android device
2. Now simply look for "Bubble Level"
3. The Bubble Level checker now appears as the first result/card
Note that this Bubble Level feature on the Google search is now the best and most accurate option you may have, but it's definitely the easiest, fastest and reliable enough.
If you insist on installing a 3rd party app, search the Bubble Level in the Play Store