The short answer
Usually, after a check. Might hold something you care about. Look inside before removing it.
What is it?
Each folder in ~/Library/Android/sdk/platforms is the Android SDK for one API level (android.jar and related files), used when a project compiles against that level. Older levels stay installed when you raise compileSdk, and each typically takes from about 100 MB to a few hundred megabytes.
SDK platforms for older API levels. The two highest are kept; a project targeting an older level downloads it again.
What happens if you delete it?
A project that still compiles against a removed level downloads it again on the next build through the Android Gradle plugin, or you can reinstall it in the SDK Manager.
How to remove it properly
In Android Studio, open Settings › Languages & Frameworks › Android SDK › SDK Platforms and untick the API levels you no longer compile against; or run sdkmanager --uninstall "platforms;android-<level>" in Terminal (permanent).
Use the tool’s official command: sdkmanager --uninstall "<package>"
- MoreRoom keeps the newest 2 and suggests the older ones.
How MoreRoom helps
MoreRoom recognises this item and labels it “Review first”: it shows what’s inside, its size and last use, so you can decide. Nothing is removed without your say, and everything goes to the Trash first, with Undo.
When the tool is installed, MoreRoom runs its official command for you (sdkmanager --uninstall "<package>") instead of deleting files — and tells you that this step can’t be undone.
Frequently asked questions
Can I delete old Android SDK platforms (API levels)?
Usually, after a check. Might hold something you care about. Look inside before removing it. A project that still compiles against a removed level downloads it again on the next build through the Android Gradle plugin, or you can reinstall it in the SDK Manager.
Will Android SDK platforms (old API levels) come back after I delete it?
Yes. A project that still compiles against a removed level downloads it again on the next build through the Android Gradle plugin, or you can reinstall it in the SDK Manager.
How do I remove Android SDK platforms (old API levels) properly?
In Android Studio, open Settings › Languages & Frameworks › Android SDK › SDK Platforms and untick the API levels you no longer compile against; or run sdkmanager --uninstall "platforms;android-<level>" in Terminal (permanent).