# Chess - credits and notes

**The game.** Chess as codified in the FIDE Laws of Chess: the movement of the six pieces, castling and
its four conditions, en passant, promotion, check and checkmate, stalemate, the dead-position rule,
the fifty-move and threefold-repetition claims and, since 2014, the automatic seventy-five-move and
fivefold-repetition draws. The way chess is presented on the web was standardised by the popular chess
sites: a flat two-dimensional board with coordinates, click or drag to move, legal-move dots, last-move
and check highlights, a move list in algebraic notation, computer levels, flip board, FEN and PGN.

**This implementation** (https://chess.skillsafe.ai/) is independent work written from the published
rules and specifications. The move generator is verified against the perft node counts published on the
Chess Programming Wiki (initial position, "Kiwipete" and positions 3 to 6), and against a second,
deliberately different legality checker; notation follows Wikipedia's articles on algebraic notation,
Forsyth-Edwards Notation and Portable Game Notation, and the PGN import was tested on the Opera Game
(Morphy v Duke of Brunswick and Count Isouard, Paris 1858). The computer opponent is an alpha-beta
search with iterative deepening, quiescence search, a transposition table and piece-square tables,
running in a Web Worker at eight time-limited levels.

Additions that go beyond the reference conventions, labelled as such on the page: the game in progress
survives a reload, statistics are kept per computer level, deep links open a game at a level and colour,
and the sounds are synthesized in the browser.

Everything here - the piece set (drawn from simple shapes), the board colours, the sounds, the help text
and the code - is original work. Nothing was copied from Lichess, Chess.com or any other chess site or
program, and this page is not affiliated with or endorsed by FIDE, Lichess or Chess.com. "Chess.com" is a
trademark of its owner; "Lichess" is the name of the lichess.org project.

The code is released under the MIT licence; see LICENSE.txt.

References (all read through the MediaWiki API on 2026-09-05): Wikipedia, "Rules of chess", "Draw
(chess)", "Fifty-move rule", "Threefold repetition", "Algebraic notation (chess)", "Forsyth-Edwards
Notation", "Portable Game Notation", "Opera Game"; Chess Programming Wiki, "Perft Results"
(https://www.chessprogramming.org/Perft_Results).