Chess

Instructions

Welcome to "Scratch Chess - Game of Kings". FAQs: - "There is a bug!" Unlikely, 375k visits, no known issues. Consult experienced player, read instructions. - "Why invalid move?" Likely keeps/puts you in check. - "I still found a bug!" Please describe in detail, and click "Export", then copy & paste FEN (board) or PGN (moves) data into a comment. - "Too difficult!" Switch to level Easy 1 or 2, at which the engine partly makes random moves. - "Too easy!" Play level Difficult on TurboWarp (a Scratch runtime 20x faster than Scratch 3): https://turbowarp.org/148769358 If you win against level Difficult, please copy/paste PGN data for analysis (click "Export"). You might have to split PGN data into multiple comments. Scratch is not well suited for CPU-intense calculations (interpreted, missing language features like bitwise operations, slow by design), that is why a Scratch chess engine will always have limited playing strength. TurboWarp is faster, but still has to emulate Scratch, hence has to impose similar restrictions. - "Too slow" The GoK engine is think time bound on levels Medium and Difficult, and takes exactly as long as designed (10 seconds or ply4 search finished (Medium) resp. 20 seconds midgame / 15 seconds endgame (Difficult)). On Easy and Blitz levels, response time is 0 to 3 seconds on decent hardware, making GoK the fastest Scratch engine. Scratch is inherently slow due to its design and interpreted nature. - "How to castle?" Move the king two squares towards the rook; king must not be in check, none of the passed squares must be attacked, and neither king nor rook must have moved before. - "Board is set up incorrectly" Maybe you mixed up king and queen. - "King and queen move the wrong way" Maybe you mixed up king and queen? - "King and rook moved at the same time" That's called 'castling', and is a valid move. - "Opponent pawn captured my pawn which had already passed it by moving two squares before!" That's called 'en-passant', and is a valid move. - "Why is it a draw when the engine mainly has its king left and I still have pieces?". Most likely draw by stalemate (no legal move but also not checked) - "How do I copy FEN or PGN data?" Click "Export", triple-click FEN or PGN data, press Ctrl-C (Windows) or right-click / select "Copy". - "How to play en-passant?" Move your pawn diagonally by one square, behind the opponent pawn which just moved two squares. - "What does the black/white bar on the right side of the board indicate?" It shows the current evaluation of the board, so either black's or white's lead in the game. - "Can you increase the engine's playing strength?" It has been tuned a lot already, and we probably reached the end of the rope now. A Scratch chess engine will never play at the level of one implemented in C/C++, Java or JavaScript. Scratch is slow due its interpreted nature, every variable access triggers a table-lookup by name, it doesn't have bitwise operations for bitboards, and uses variants with constant value conversions, etc. Difficulty levels (on Scratch 3): - Easy 1: searches 1 ply plus 3 subsequent captures, makes many deliberate mistakes - Easy 2: searches 1 ply plus 3 subsequent captures, makes some deliberate mistakes - Blitz 1: searches 2 plies plus 10 subsequent captures / checks - Blitz 2: searches 3 plies plus 10 subsequent captures / checks - Medium: think time 10 seconds (if ply 4 reached); searches ca. 4 plies plus all subsequent captures / checks during midgame, more during endgame (on fast systems) - Difficult: think time 20 seconds for midgame, 15 seconds for endgame (if ply 4 reached); searches ca. 4-5 plies plus all subsequent captures / checks during midgame, more during endgame (on fast systems) - Difficult (competition mode, press 'c'): think time 40 seconds; searches ca. 5-6 plies plus all subsequent captures / checks during midgame, more during endgame (on fast systems) The fast TurboWarp runtime will add ca. 4 plies on Medium and Difficult. Press 'c' to toggle 40 seconds think time on Difficult Press 'd' for debugging info (evaluation, search depth, NPS, MPS) Press 'p' for profiler mode (CPU time spent per function and search depth, number of transposition table hits) Press 't' to set transposition table cache size BUG REPORTS: Please describe exactly what happened, and if possible provide exported board data: Click "Export", then look for the FEN data, select the text by triple-clicking it, copy it to the clipboard and paste it to the bug comment. Alternatively you can also export the move list in PGN format. Please also report the difficulty level. Before you post a bug, go sure it really is a bug and not a misunderstanding, e.g. you may want to consult an experienced chess player beforehand. Thank you! Remix instructions: Remix BEFORE playing, otherwise lists will be too large for saving. Or run the "RUN_BEFORE_SAVING" custom block.