title: How to install Android SDK r21 with compatible platform-tools and packages
body: <p>For an old Unity project I need Android SDK r21. I can successfully install it from <a href="http://dl.google.com/android/installer_r21-windows.exe" rel="nofollow">here</a>.</p>
  
  <p>Unfortunately I cannot install the platform-tools r19.0.1 from the SDK manager (Package cannot be used due to error: platform-tools folder is missing aapt.exe ...).</p>
  
  <p>Apparently the SDK r21 is incompatible with platform-tools r19.0.1. Unfortunately I am unable to download an older version or the individual Platform SDKs that I need for the Google APIs. </p>
  
  <p>I guess I need an older version of the repository.xml, but I have no idea how to find it.</p>
  
  <p>Any advice?</p>
  
  <p>Thanks a lot!</p>