Random server and client seeds are generated and you can always change your client seed.
Before you specify your own seed, you are shown the SHA256 hash of the server seed that will be used alongside whichever seed you pick.
Changing the client seed used will also reveal the previous server seed, which you can then verify was the seed we hashed and showed you.
Server seed, client seed and nonce ( number of bets made with current seed pair ) are used to generate your roll (nounce is increased by 1 each roll).
Use this primedice provably fair checker to verify if your bet is tampered, you just need to insert Server Seed, Client Seed and Nonce: