Dominoes

The set is the double six: twenty-eight tiles, every pair of numbers from double blank to double six exactly once. Whoever holds the highest double leads with it, and if nobody has one the highest tile leads instead.

After that, the chain has two open ends, and a tile can be added at either end if one of its halves matches the number showing there. A tile that fits both ends is two different moves, and choosing which is most of the game — the number you leave showing is the number your opponents have to answer.

A round ends the moment somebody lays their last tile, and they score the total pips left in every other hand. It can also end with nobody able to go at all, which is called a blocked table: then the lowest pip count wins and scores the others’ pips, and if the lowest count is shared, nobody scores at all.

Zerdly’s preset, stated rather than left to be discovered: the highest double leads, or the highest tile if there is no double. Seven tiles each at two players and five each at three or four. The winner of a round scores the pips left in every other hand. A blocked round goes to the lowest count, and a shared lowest count scores nothing for anybody rather than being broken by seat order, which would quietly favour whoever happens to sit first.

Draw and Block are genuinely different games rather than a difficulty setting. In Draw, a player who cannot go takes tiles from the boneyard one at a time until one fits or it runs out; in Block there is no boneyard to draw from and they simply pass. Block is shorter and much sharper, because every tile you cannot place is one the table now knows you do not have.

Show playable marks outlines the tiles in your hand that can actually go; it is on to begin with, and turning it off does not change what is legal. Track passes writes down what everybody has given away by passing — it is off to begin with, because a strong player keeps that in their head and it is a real advantage rather than a convenience. Hint suggests a move, working only from what your own seat can see. Sound can be turned off at any time; nothing here is conveyed by sound alone. A match in progress is saved as you play and is waiting when you come back — including a round you are losing.

Versus the computer gives you four strengths, and each does something different rather than simply thinking for longer. Gentle plays whatever fits. Casual keeps itself playable and watches which numbers you have passed on. Steady deals out the tiles it cannot see, many ways over, and plays the odds. Sharp works those same possible tables out exactly rather than estimating them, and once nothing is left face down in a two-handed round it plays the ending perfectly, because at that point there is nothing left to guess.

Players at one device takes the computer out of it. Because this game has something to hide, the tiles come off the screen between turns and stay off until the next player says they are looking — otherwise passing the phone round would mean showing everybody everything. These games are counted but not scored: everybody is at the same table, so there is nobody for Zerdly to call the winner.

Watch what people cannot play. A pass is the most informative thing that happens in dominoes: it tells the whole table that somebody holds nothing showing either open number, and that fact stays true for the rest of the round. Leaving that number showing again is how you make them pass twice.

Keep yourself playable. A hand full of one number looks strong and is fragile — the moment that number stops showing, you are passing while everybody else scores. Spreading across the numbers still on the table is usually worth more than shedding your heaviest tile, which is the opposite of the advice most people are given.

Doubles are the hardest tiles to place, because only one number will take them. If you are holding one late, look for the chance to play it while its number is still showing at both ends rather than hoping it comes round again.

The whole game runs in your browser. The opponent thinks on your own device, in a background thread so the page stays responsive while it works. No account is needed and nothing about your game is uploaded.

Your record, your saved match and your sound, motion and assist settings are stored in this browser only. The saved match holds the shuffle and the moves rather than the tiles, so there is nowhere in your browser that anybody’s hand is written down. Nothing here asks for a name or an email, and the button on this page removes all of it — and only this game’s share of it.

Is it really free, and do I need an account?

Yes, and no. There is no sign-up, no trial and nothing to buy. The game runs in your browser and never sends your moves anywhere.

Can the computer see my tiles?

No, and that is enforced rather than promised. The opponent is only ever handed what your seat could work out for itself: the chain, how many tiles everybody holds, how many are face down, and what has been played. There is no way to give it the real hands, because nothing in the opponent accepts them. A test builds two rounds that look identical to it and are completely different behind the screen, and checks that it plays the same tile in both.

Why did the computer suddenly know I had no fours?

Because you passed while a four was showing, and that told the whole table. It is not a peek, it is arithmetic anybody at the table can do — and you can do it too. Turn on Track passes to see the same notes it is keeping.

How strong is the strongest opponent?

Stronger than the other three, and not by as much as you might expect. Dominoes hides so much that guessing harder stops helping: past a certain point the opponent is estimating the same uncertain thing more precisely rather than playing better. Sharp gets round that where it can by working a position out exactly instead of estimating it, and it plays the end of a two-handed round perfectly once the boneyard is empty, because at that point there is nothing left to guess at.

Can somebody read my hand out of the browser?

No. A saved game holds the shuffle it was dealt from and the moves that have been played, and the hands are worked out again when you come back. There is nowhere in local storage that the tiles are written down.

Where is my progress kept?

In this browser, and nowhere else. Each table keeps its own record, because a two-handed Block match and a four-handed Draw match are not comparable. Clearing your browser data, or using the button on this page, removes all of it permanently.

• MancalaSow the stones, chain extra turns, and sweep the board.
• Nine Men's MorrisLine up three and take a piece. Six opponents and proved puzzles.
• GomokuFive in a row, two board sizes and a daily puzzle.