How the generator builds a fair hex board

A "seed" is a 32-bit integer fed into a deterministic pseudo-random number generator (PRNG). The same seed always produces the same sequence of numbers, which means the same shuffle of terrains, the same shuffle of number tokens, and ultimately the same board. Together with the chosen mode and rule flags, the seed is encoded into a short URL-safe token like /board/3setby9.

They are pseudo-random — generated by a deterministic algorithm seeded with a 32-bit integer drawn from a cryptographically-strong source. This means the board is statistically indistinguishable from a true random shuffle, but is reproducible from its seed. The benefit: you can share boards via URL.

A purely random Catan board can have two reds touching, two 12s touching, three forests in a row — anything goes. A balanced board obeys adjacency constraints: by default the official red-number rule, plus optional rules around extreme numbers, identical numbers, and identical resources. This generator produces balanced random boards by default.

It's a backtracking placer. The terrain bag is shuffled and placed hex-by-hex; if a candidate violates an active rule the placer tries the next item. The number-token pass works the same way. If the placer dead-ends, the entire attempt restarts with a fresh shuffle. Up to 400 attempts are made before falling back to a relaxed pass that guarantees a board.

Rule flags are encoded into the seed token, alongside the mode and the RNG seed. So /board/3setby9 with red-touching enabled is a different URL from the same RNG seed without it — the boards differ slightly. This guarantees that anyone who opens the URL sees the exact same board.

For the four supported modes — Classic, 5–6 expansion, Seafarers, Seafarers 5–6 — yes. Each produces a layout based on the canonical scenario from that mode's rulebook. Custom scenarios (specific Seafarers variants, Cities & Knights variants) aren't directly supported but can use the underlying landmass.

Not currently. The implementation uses a deterministic mulberry32-style PRNG, axial hex-grid coordinates, and a backtracking constraint placer in PHP. We may open-source the core algorithm in future.

Generate a board with all four adjacency toggles in their default (off) state — that gives you the strict tournament-balanced setup. Share the resulting URL with all participating tables, and everyone plays the exact same map. Print the PNG export if you want a physical reference.