Sources and verification

Sources consulted

• FIDE Laws of Chess taking effect from 1 January 2023 (new tab) (International Chess Federation (FIDE)): how the pieces move, castling, en passant, promotion, checkmate, stalemate, dead position, draws on claim and automatic draws
• Portable Game Notation Specification and Implementation Guide (new tab) (PGN standard (public copy)): standard algebraic notation for moves (SAN), PGN format for games and FEN format for positions

Links checked on October 30, 2026. FIDE remains the reference for any question of arbitration; the site describes the rules as the app applies them.

How the examples are verified

The site's 11 positions, including those of the 6 exercises, and 3 short sample games are checked by two programs before each publication:

• the app's own rules engine, unmodified, which calculates legal moves, checkmates, stalemates, insufficient material and draws;
• a second program, written separately for this site, which redoes the same calculations; the slightest disagreement blocks publication.

What is checked: each position is legal (one king per side, no pawn on the first or last rank, possible castling rights and en passant), each move cited is allowed or forbidden as the text says, and each number shown is recalculated or reread in the app's code.

Playing tips are presented as rules of thumb that depend on the position, separate from the fixed rules. Found a mistake? Write to us via the contact page.