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
I found these instructions in a comment.
Download the newest version of ADT and use your existing workspace. This is actually the least pain-full upgrade you'll ever do. It didn't mess with the .android folder so I still had my original debug key. Only things missing were a couple of add ons I hardly ever use and they are easily installed into the new version.
Note don't install into your existing adt folder create a new folder so you can still fall back if the new install doesn't work.