Shogi Game

A real Shogi rules engine rather than a chess reskin

Shogi shares the goal of protecting a king, but the game changes dramatically because captured pieces can return to the board for the player who captured them. This specialist therefore uses a dedicated 9×9 board model, separate piece movement, reserve hands, promotion rules and drop legality. Every displayed destination comes from that rules engine and is filtered again for king safety before it reaches the interface.

Captured pieces become usable reserve pieces

When you capture a rook, bishop, gold, silver, knight, lance or pawn, the captured piece changes sides, loses any promotion, and enters your hand. On a later turn you may drop a reserve piece onto a legal empty square instead of moving a board piece. That rule makes material unusually dynamic: a piece that leaves the board is not necessarily gone from the game, and an apparently quiet reserve can create an immediate attack.

Promotion depends on the far three ranks

Rook, bishop, silver, knight, lance and pawn can promote when a move starts or ends inside the opponent’s three-rank promotion zone. The app offers both legal versions when promotion is optional. It also enforces mandatory promotion where an unpromoted piece would otherwise have no future legal move: pawns and lances must promote on the last rank, while knights must promote on the last two ranks.

Promoted pieces do not all move the same way

A promoted rook becomes a dragon and keeps its long rook movement while gaining one-step diagonals. A promoted bishop keeps its long diagonal movement and gains one-step orthogonal moves. Promoted silver, knight, lance and pawn move like a gold general. Capturing any promoted piece demotes it before it enters the capturer’s hand, so reserve pieces always return in their base form.

Nifu blocks a second unpromoted pawn on the same file

A pawn drop is not legal when you already have an unpromoted pawn on that file. The engine checks the entire file at the moment the drop list is generated. A promoted pawn does not count as an unpromoted pawn for this restriction, which means the file can become available again after the original pawn promotes or is captured.

Dead-rank drops are filtered before you can select them

A pawn or lance may not be dropped onto the final rank because it would have no legal forward move. A knight may not be dropped onto either of the final two ranks for the same reason. Instead of allowing an impossible drop and showing an error afterward, the browser removes those destinations from the legal list in advance.

Pawn-drop mate protection is part of legality

Shogi has a special restriction against delivering immediate checkmate by dropping a pawn. The local move generator tests a checking pawn drop and rejects it when the opponent has no legal reply. That test is part of the move engine, not a message layered over an otherwise permissive board, so Hint and AI use the same restriction as manual play.

King safety is checked after every move and drop

Piece movement alone is not enough to make a move legal. The engine applies each candidate to a cloned position and rejects it if the moving player’s king would remain or become attacked. This handles ordinary checks, discovered attacks, defensive drops and capture responses without giving the interface a separate approximation of legal play.

Black moves first and the board can orient to either side

Standard Shogi begins with Black, or sente, to move. Practice can place you as Black, White or a seeded-random side. When you play White, the board rotates so your pieces remain closest to you while the internal coordinates stay fixed. Reserve hands and piece orientation update with the same player-side choice.

Easy, Standard and Hard share one legality engine

The three browser-local AI levels never receive different rules. Easy uses wider seeded variation among legal moves. Standard prefers material gains, promotion, checks and useful reserve activity. Hard narrows its choice toward the strongest score from the same transparent heuristic evaluator. These labels are product difficulty settings, not dan or kyu ratings and not claims of professional engine strength.

Practice seeds make sessions reproducible

Opening a Practice game without a seed creates one and writes it into the URL. That seed stabilizes side assignment when seeded-random color is selected and stabilizes AI tie-breaks. Your moves still determine the game tree. Refresh or autosave therefore returns to the same session identity, while Fresh Practice intentionally starts another seed.

Hint, Undo and Restart have an explicit study boundary

Hint marks the game Assisted and highlights a legal suggestion from the strongest local heuristic. Undo restores the exact state from before your previous decision so the computer reply is rolled back with it. Restart rebuilds the same deterministic opening contract. These features are valuable for learning, but the result is not presented as unaided once you use them.

Repetition handling is disclosed instead of overstated

For local browser play, four identical positions with the same side to move and the same reserve hands end as a draw. That protects the app from endless loops and matches the core repetition concept. The page does not claim to reproduce every tournament-specific perpetual-check adjudication detail; that limitation is stated directly rather than hidden behind a generic “official rules” label.

Daily Shogi remains a separate specialist habit

The date-stable Daily mode uses its own seed, side assignment, autosave, history and streak. Shogi is not inserted into the frozen Today’s 6 rotation and does not write a result into the main Daily `days` state. That separation is protected by cumulative QA alongside the other specialist games.

Private browser practice without invented global telemetry

Game state, reserve hands, autosave, wins and Daily history stay in this browser. There is no account dependency, external Shogi engine, global leaderboard, fake dan or kyu rank, or invented percentile. There is also no wagering, chips, prizes, stakes or paid-random mechanics. The product is designed around legal play, replayable study and understandable rules.