Most of the time the tool is getting it right, even though it's not always free. Some domains are available for sale, but are currently squatted.

Fun fact, I just did a search for: "Evil domain registration service that will query for the best names and will register them before you can."

I found an excellent short .com that is available for a regular price. Now sure if I should grab it, now that I've already got a name. It's so tempting!