The syntax checking Web sites reviewed here can all be pointed to any Web page that have a HTTP address, so they must have been uploded to the server already.
Although they all carry out what is essentially the same task, they do it in slightly different ways and have useful additional features. I'm not going to even try to score them, as I usually do in product reviews, they are too different for such direct comparison. They all do what they are supposed to do and I can't argue with the accuracy of the reports.
None of them are as user-friendly as they could be. Bobby, comes close, but has a slightly different agenda. If you keep at arms-length from HTML, none of them are going to be of much help, but you can't blame them for that.