I've received requests from people in the past to look into 999dice's provably fair system but I never got around to doing so. I'm sorry now that I didn't.

Withholding the server seed hash until it is explicitly requested is dubious behaviour. It allows the site to cheat on all rolls except those for which the server seed hash has been requested, which will be almost all of them.

Changing the server seed for each individual roll in itself is bad enough, since it requires the user to keep extensive records and also to change their client seed every roll to be sure that they aren't being cheated. Add the hiding of the server seed hash on top of that and you really do have to wonder what's going on. Why would anyone go to such lengths to hamper their provable fairness?

Of course none of this is proof that any cheating is going on, much like how having to let your boss know when you take the afternoon off doesn't prove that he's doing your wife. But when every other company in town lets you come and go as you please without notification you have to wonder what he is trying to hide.

Also, with so many sites struggling to make a profit with a 1% house edge how does 999dice manage to profit so well with only a 0.1% edge? Players should demand an overhaul of the probably fair system as soon as possible. Ideally players will be able to verify their rolls with very little effort. Using a single client/server seed pair for as many rolls as the user likes (pioneered by Just-Dice.com in June 2013) is the industry standard.