I updated Eclipse with the new SDK tools (rev. 23), but now when Eclipse starts I receive the error:
This Android SDK requires Android Developer Toolk
For me it helped to delete Android 4.4W which is also API 20 and might be a cause for the conflict. So only install Android 4.4W or Android L until they fix it.
And (again this might only be for me) it only works in Android Studio not in Eclipse ...