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?
is it possible they can reverse code it once you click that button to be sure its "fair" once they know you checked?
like ok we know the roll = "49.50" and his client seed = "jhoitybihiopyiye"
so to get to 49.50 could they do something like this to get the correct sever seed?
49.50(roll) / jhoitybihiopyiye(client seed) = server seed
just taking a stab at it cause i know another site does the same practice