Every squares board runs on the same trick: a hundred squares, ten digits across the top, ten down the side, and nobody finds out which square is which until everyone’s already picked. That order matters more than people usually think about — if the numbers were known in advance, or could be changed after the fact, the whole board would just be a popularity contest for whoever went first.
The old way
On paper, this got solved with a hat: ten slips of paper per axis, drawn by hand in front of the room, written onto the board as they came out. It worked, as long as everyone trusted whoever was holding the hat and nobody left the room before it was their team’s turn to draw.
The digital version
GridAction runs the same idea without needing everyone in the same room. The moment a board locks — meaning nobody can claim or drop a square anymore — the server generates a random 256-bit seed and immediately publishes a short fingerprint of it (a cryptographic commitment) on the board, before any digit has been assigned to anything.
When the commissioner is ready, they draw: the server reveals the seed, and the digits are derived from it the same way every time, following a published, fixed procedure. Because the commitment was posted before the reveal, anyone can now check that the seed wasn’t swapped out afterward for one that produces a more convenient result — the fingerprint either matches or it doesn’t.
Checking it yourself
You don’t have to take the app’s word for it. The draw’s commitment, seed and the exact steps to recompute the digits from it are public — see how to verify a draw. It takes a few minutes in a browser console, and it’s the same check for every board, every time.