What is a deterministic seed?
A deterministic seed is a fixed starting value that makes a game generate exactly the same board, pieces and events every time it runs. Give every player the same seed and they play the same game — so their scores measure skill, not luck of the draw.
Most games use randomness to feel fresh: which block falls next, where the pellet spawns, how the traffic flows. That randomness comes from a generator, and a generator is started from a number — the seed. Random seed, different game every run. Fixed seed, identical game every run. Same idea as sharing a “daily puzzle” — everyone solves the same one.
On Winnly, every arena is generated from one seed shared by the whole field. In Tetraverse that means the same piece sequence for everyone; in Snake the same pellet spawns; in Death Race the same traffic. Two players who play identically would score identically; every point of difference is something someone did.
It also makes results checkable: replay the seed against a run’s recorded inputs and you reconstruct the run. That replay verification is the backbone of the fair play guarantee, and the reason “the game favored my opponent” is a testable claim on Winnly rather than an argument. It is also the honest answer to the category’s loudest worry — are the opponents real people?
For the wider picture — what makes a game skill-based at all, and the four questions to ask any app that claims it — read What is skill-based gaming?
Questions
Is a deterministic seed the same as no RNG?
Almost. A game can still use a random-number generator to build its level; the seed makes that generator produce the same output for everyone in the match. What players mean by “no RNG” is no randomness that separates one player's outcome from another's, and a shared deterministic seed is how that is achieved.
Does a seed make the game easier or harder?
Neither: it makes the game identical. The arena can still be brutally hard; the point is that it is exactly as hard for every player in it.
Can a seeded game be replayed?
Yes, and that is the second benefit: because the same seed reproduces the same game, a finished run can be replayed against the recorded inputs and checked. On Winnly that is what makes results verifiable rather than taken on trust.