How to play Chess

Chess is the great strategy game — two armies of sixteen pieces, an eight-by-eight board, and an almost limitless set of possibilities that unfold from the very first move. Here you play against the computer with nothing to install: pick your colour and your difficulty, tap a piece to see where it can go, and tap a highlighted square to move. The full rules are enforced, including castling, en passant and pawn promotion, and the board tells you when a king is in check.

The goal

Checkmate your opponent's king — that is, attack it so that it cannot escape capture on the next move. The game can also end in a draw by stalemate (the side to move has no legal move but is not in check), by the fifty-move rule, or when neither side has enough material to force mate.

How the pieces move

• Pawns move one square forward (two from their starting square) and capture one square diagonally. On reaching the far rank a pawn promotes — usually to a queen, though you may choose a rook, bishop or knight.
• Knights move in an L: two squares one way and one square at right angles, leaping over anything in between.
• Bishops move any distance diagonally; rooks any distance in straight lines; the queen combines both and is the most powerful piece.
• The king moves one square in any direction. Once per game each side may castle, moving the king two squares toward a rook and the rook to the king's other side, provided neither has moved, the squares between are empty, and the king is not moving through or into check.
• En passant: a pawn that has just advanced two squares can be captured by an enemy pawn beside it as though it had moved only one.

Choose your difficulty

Three levels set how far the computer searches. Easy looks two moves ahead and sometimes plays a careless move, ideal for learning. Medium searches three moves ahead. Hard searches four moves ahead with alpha-beta pruning and a material-plus-position evaluation, and will pounce on hanging pieces and tactical mistakes.

Strategy and tips

Open with the centre: pushing a central pawn and developing your knights and bishops toward the middle gives them the most squares and the most influence. Castle early to tuck your king into safety behind its pawns. Try not to move the same piece twice in the opening or to bring the queen out too soon, where it can be chased around and lose you time. In the middlegame, count the attackers and defenders on a square before you trade, look for pieces that are undefended ("hanging"), and keep your king safe. In the endgame, activate your king and push your passed pawns toward promotion.