Every roll is HMAC-SHA256(serverSeed, clientSeed:nonce). Before a round the house publishes only the SHA-256 commitment of its secret server seed. When the round ends the raw seed is revealed, so you can recompute every roll yourself and confirm the result was fixed before you bet — not after.
The exact formula
roll = int(HMAC_SHA256(serverSeed, `${clientSeed}:${nonce}:trondice`)[0:8], 16) mod 10000
You win when low×100 ≤ roll < high×100. The payout is 99 / (high − low) — a flat 1% house edge. The same code runs on this page, in the game, and on the server.