Dominoes

Everybody draws a hand from the shuffled set and the player holding the highest double lays it down. From then on a turn is one tile: pick something from your hand that carries a number showing at one of the layout's open ends, and lay it against that end so the matching halves touch. If nothing in your hand fits, you draw from the boneyard — one tile at a time, and you keep drawing until something fits or the boneyard runs dry. Only then do you pass. The first player to lay their last tile takes the game.

The rule people most often play wrong is the one about drawing: a hand that holds a legal tile has to play it. You may not fish in the boneyard to improve a playable hand. On this board that rule is enforced rather than trusted — the Draw button is dead while any tile in your hand fits, and the engine refuses the move even if you find another way to ask for it.

A double is never laid lengthwise. It goes down crosswise, sideways across the line, and that has two consequences most casual implementations miss. First, both of its halves are exposed, so a double sitting at an end counts twice — a four-four at the end of the line shows 8, not 4. Second, the very first double played becomes the spinner: the line runs through it, and its two halves stick out either side, so the layout can eventually grow in four directions instead of two.

The branches off the spinner do not open immediately. The line has to be built past both sides of the spinner first; until then the spinner's two halves are pips that count but cannot be played on. That is also why a six-six opening reads 12 and not 24: the sides of the spinner that the line attaches to show no pips at all, so there is nothing there to count beyond the two halves.

Five tiles, 75 points. Note that the spinner's two sixes keep paying the whole way down that table — nothing has been laid on them — while both line ends are built on twice. Until a double appears at all there is no spinner, only two plain ends, and the layout can never show more than 12.

All Fives — often called Muggins — is the variant most American players actually play, and it is one extra rule: every time your play leaves the open ends totalling a multiple of five, you score that total. A double-five opening is worth 10 straight away. A layout reading 23 is worth nothing; turn one of its fives into a two and the same layout is worth 20 to whoever did it.

This is where the geometry stops being pedantry and starts being the game. With two ends the most the layout can show is 12, so the reachable scores are 5 and 10. With a spinner and four ends, 15, 20, 25 and 30 come into range — and the counts move in jumps, because a double swaps a single number for twice that number in one move. A four-four laid on a 4 does not add 4 to the count; it adds another 4 on top of the one that was already there.

At the end of the hand the winner also takes what everybody else is still holding, less whatever is left in their own hand, rounded to the nearest five: 22 pips becomes 20, 23 becomes 25. Real matches are played to 150 or 250 points over many hands. This board scores one hand at a time and shows the running totals for every seat, so you can see who was ahead on points even when somebody else went out.

When the boneyard is empty and a player has nothing that fits, they pass. If every player passes in turn, the hand is blocked: no tile anybody holds can go anywhere, so the hand is settled on pips instead. The lowest total wins it and scores the difference between their hand and everybody else's. If two hands tie on the lowest total, nobody takes it and nobody scores.

Blocked hands are the exception rather than the rule, which is worth knowing because it changes how much your pip count is worth defending. Played out two-handed by the opponents on this board, about one deal in ten ends blocked under plain block scoring, and nearer one in sixteen once All Fives is on; the rest end with somebody laying their last tile. That is why hoarding low tiles to survive a block usually costs more than it saves.

Two-handed, the boneyard is as big as the two hands together, so a bad opening hand is recoverable: a run of draws can more than double the seven you were dealt before the reserve is gone. At four seats there are only eight tiles in reserve and a hand can never pass 13, so there is far less room to draw your way out of a bad start — a four-handed deal ends blocked more often than a three-handed one, and the hand you were dealt is much closer to the hand you have to win with.

About 9.8% of seven-tile hands contain no double at all — roughly one hand in ten. For nobody at a two-handed table to hold one is far rarer: it happens in exactly one deal in 345, and that is the only time the highest-double rule cannot be used. When it happens the heaviest tile opens instead, weight being the pip total with the larger half breaking a tie.