The rules, including the ones that get fudged
Men move one square diagonally forward and capture by jumping an adjacent enemy piece to the empty square beyond. Captures are compulsory: if a jump exists anywhere on the board, a jump is the only legal move. If the piece can jump again from where it lands, it must — the whole chain counts as a single move.
Reaching the far rank crowns the piece a king, which moves and jumps in all four directions. And crowning ends the move: a man that reaches the back rank by jumping stops there, even if more jumps appear available. That is English rules, and it is the detail most browser checkers games get wrong. Our move generator is checked against the published position counts — 7, 49, 302, 1469, 7361, 36768, 179740 and 845931 positions at depths one through eight — so the rules here are not a matter of opinion.
A player with no legal move loses, which means being blocked is exactly as fatal as being captured.
The opponent
Hard searches seven plies with alpha-beta pruning and only stops evaluating in quiet positions, so it will not hand you a piece and it will find the two-for-one shots that decide most casual games. Easy plays loosely on purpose. Learn mode shows what the engine would play before you move.