How shuffles work at cards4.net

Our random number generator

For the solitaire variants supported by the verifier, the card engine uses Erlang's :rand module and exsplus algorithm to shuffle cards. This pseudorandom generator is not cryptographically secure. Each deal has a 63-bit integer seed. With the same seed, game variant, and shuffle implementation, the starting position can be reproduced. Our server-side verifier checks reproducibility, not how the seed was selected.

Seeds are displayed as 13-character Crockford Base32 strings (e.g. 0004FKQR2MXZE). This encoding avoids visually ambiguous characters.

Daily challenge seeds are drawn from our pre-validated solvable library — every daily is guaranteed winnable. The seed for each daily is derived deterministically from the game, variant, and UTC date, so the same deal is served to every player worldwide on that day.

See the seed format documentation for full details.

Verify a seed

Paste any seed into the verification tool on this page to see the exact deal it produces. The result is computed server-side and is identical to what you would see in the game, so you can confirm for yourself that a given seed always yields the same shuffle.