Full backgammon on a portrait board that fits a phone. Play the computer on Easy, Medium or Hard, or take turns with a friend on one screen.
Backgammon is a race game for two: each side moves 15 checkers around a 24-point board using two dice, and the first to bear all 15 checkers off the board wins. Each side travels in its own direction, from its 24-point down to its 1-point, which is the last point of its home board (points 1 to 6). You start with 2 checkers on the 24-point, 5 on the 13-point, 3 on the 8-point and 5 on the 6-point, and so does the computer from the other side, so each side starts 167 pips from home (a pip is one step of one checker). On your turn you roll two dice and move by each number, using one die per checker move: a 5 and a 3 can move one checker 8 points or two checkers 5 and 3. Doubles are played four times. At the start each side rolls one die, the higher roll goes first and plays those two numbers as its first turn. This page draws the board upright, with your home board at the bottom left, so the whole game fits a phone.
A point with two or more checkers of one colour is made, and the other side cannot land there. A point with one checker is a blot. If the other side lands on a blot it hits it: the checker goes to the bar, in the middle of the board, and its owner must bring it back in before making any other move. A checker enters on the point that matches the die, counted from the far end: a 6 enters on the opponent's 6-point, a 1 on their 1-point, and it can only enter on an open point or a blot. If every entry point is blocked, the turn is lost. You must play both dice if you can. If only one die can be played you must play the larger one, and you must always play as many dice as possible. In the app these rules are enforced for you: tap a checker and only the points you can really move to are lit, and a move that would waste a die is not offered.
You may start bearing off only when all 15 of your checkers are in your home board and none is on the bar. A die bears off a checker from the point with that number. If the die is higher than your highest occupied point, it bears off a checker from that highest point instead; otherwise you must move a checker inside the board. The first side to bear off all 15 wins 1 point. If the loser has not borne off a single checker, it is a gammon and the winner scores 2. If the loser also still has a checker on the bar or in the winner's home board, it is a backgammon and the winner scores 3. The doubling cube is optional here and off by default. When it is on, before rolling you may offer to double the stakes; the other side takes, and then owns the cube, or drops and loses the points at stake. The cube goes 1, 2, 4, up to 64, and multiplies gammons and backgammons. The running score across games is kept next to the board; match play is not included.
Easy picks a random legal turn about a third of the time and otherwise leans toward hitting and toward leaving fewer blots, so it is beatable. Medium looks at every legal turn and scores the resulting position by pip count, blots weighted by an estimate of how likely a hit is over the 36 dice outcomes (an approximation that ignores some forced-move rules), made points, primes, anchors, and checkers stacked or on the bar. Hard uses a small neural network that learned by playing against itself, ranks every legal turn with it, then searches the best few two moves deep, averaging over the opponent's 21 different rolls. Each move is limited to a fraction of a second, and the search runs in the background so the page stays responsive. Hard is a solid player and not an expert engine: it does not know every opening or endgame position. The dice come from your browser's secure random number generator for both sides, and the computer plays the numbers you can see. The game in progress, your settings and your records per level stay in this browser; moves are not uploaded.
Each side rolls one die. The higher die goes first and plays both numbers as the first turn; equal dice are rolled again. For example, if you roll 5 and the computer rolls 2, you start and play 5 and 2. This page does the opening roll for you when you press New game.
You must play as many dice as the rules allow. If only one die can be played you must play the larger one when either can be. Doubles are four moves, and if only two of the four can be played, you play those two. The app only lights moves that keep the maximum number of dice playable.
When all 15 of your checkers are on points 1 to 6 and none is on the bar. A 4 bears off from the 4-point. A 6 with nothing on the 6 or 5 bears off from your highest point, say the 4. If a checker is still on a higher point, a smaller die must be played inside the board instead.
A gammon is a win where the loser has borne off no checkers, worth 2 points. A backgammon is a gammon where the loser still has a checker on the bar or in the winner's home board, worth 3 points. A normal win is 1 point. Each is multiplied by the doubling cube value, so a gammon with the cube at 4 scores 8.
Turn Doubling cube on in the menu. Before you roll you can press Double. The computer takes if it wins at least about 1 game in 4 and drops otherwise, and a drop gives you the current cube value, such as 2 points. After a take the cube is on the new value and owned by the taker, who is the only one who can redouble.
The dice come from your browser's secure random number generator, 1 to 6 with equal chance, and the computer cannot see or change a roll. For two people choose 2 players in the menu: Purple and Teal take turns on one screen and the board turns to face whoever is playing. Games against a friend are not counted in your records.