Google has had song duplication detection in the web version of Google Play Music for a while now, but it was strangely absent in the Android app for the longest time. No longer.
A recent update seems to enable the feature, with one person noting it was in the app as soon as 2 versions ago. It’s simple: if Google detects you’re adding a song into a playlist that already exists, they’ll alert you and give the option to either go ahead with adding it or skip it.
It’s a life saver for folks with massive playlists where it’s hard to keep track of every single song in it. All you’ll need is the latest version of the app so go find it at Google Play.