Checkers
Checkers in the browser, on a phone or tablet: play against the computer, or pass one device between two people. It plays American rules as written. If you can jump, you must, a jump chain has to be finished, and being crowned ends the move.
How to play
Move diagonally forward onto a dark square. Jump an enemy piece to take it, and reach the far row to be crowned — a king moves and jumps in all four directions.
If you can jump, you must. The board marks the piece that will come off, so the forced move is never a mystery. Chain jumps are one turn: keep tapping until the piece runs out of victims. Being crowned ends the move there and then.
Tap a piece, then tap where it goes. You lose when you have no legal move left.
The ladder
Every win moves you up a rung, and the opponent both looks further ahead and stops throwing games away. A draw keeps you where you are. A loss ends the run.
ROOKIE looks one move ahead and often forgets to. CLUB, from level 3, takes whatever you leave hanging. SHARP, from level 5, sets up trades several moves out. RUTHLESS, from level 8, stops making mistakes. MERCILESS, from level 12, reads the endgame before you have entered it, and keeps looking deeper as you climb.
A win pays 150 points per level plus 25 for each of your pieces still standing. Your best score and level are kept in your browser. Pass-and-play games are not recorded.
How the computer plays
When you play against the computer, it searches ahead through its moves and your replies, skipping lines it can already prove are worse, and it has well under a second to decide.
Difficulty is two dials: how far ahead it looks, and how often it ignores what it saw. The easier opponents are not crippled, they occasionally throw away the right answer. That makes them miss things the way a person does instead of playing strangely.
Two kings can chase each other forever, so the game calls a draw after forty moves each with no capture and no ordinary piece moving.
Checked against the numbers
Captures are compulsory, but you choose which one. American rules do not force the longest jump, unlike Italian draughts, and a chain is only offered once it cannot continue, so the game never has to ask whether you meant to stop.
The move generator is tested by counting every possible game from the opening position, one to six moves deep, and matching the published totals: 7, 49, 302, 1,469, 7,361 and 36,768. A single mishandled crowning or edge of the board would throw those numbers off.