Yeah, there are no sites to do this
Some things to consider
1) Say it loud and see if it easy to pronounce
2) How many ways are there to spell it? ie Wooby, Woobi, Woobie, Woobey, etc
3) If you were driving and heard the domain on the radio., would you go home and type the correct url on your first go? It your answer is yes, its quite a good brandable