In simple words:
Every time Google releases a new version of Android, a corresponding Android SDK is also released. To be able to write programs with the latest features, developers must download and install Android version’s SDK.
Android SDK is classified into 2 groups:
- Android SDK Tools : Android SDK Tools is a component for the Android SDK. It includes development and debugging tools which all are essential for any Android app(or application) development. So complete kit for software development required for development of an Android app(or application).Its important tools are Android SDK Manager, Android Virtual Device Manager, Android Emulator, etc.
- Android Platform Tools (or Android SDK Platform Tools) : Android SDK Platform-Tools is a component for the Android SDK. It is customized to support features of latest version of Android. It gets updated whenever we install a new Android SDK Platform. Each update of the Android Platform Tools is backward compatible. Android Platform Tools include aidl, adb, aapt, dexdump, and dx. And these tools are mostly called by ADT and Android build tools. So very rarely it is required to invoke these tools directly.
Note : Android SDK Platform Tools is a component of Android SDK not the Android SDK Platform. Android SDK Platform Tools just get updated by updating Android SDK Platform.