Welcome to "Scratch Chess - Game of Kings". FAQs: - "There is a bug!" Unlikely, 760k visitors, 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 makes semi-random moves. - "Too easy!" Play level Difficult on TurboWarp (a Scratch runtime 50x 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" On slow systems it is recommended to select a lower playing level. The engine is think time bound, and takes exactly as long as designed (10 sec (Medium) resp. 25 sec midgame / 15 or 10 sec endgame (Difficult), or up to twice as long, when minimum search depth not finished). On Easy and Blitz levels, response time is 0 to 4 seconds. Scratch is inherently slow due to its design and interpreted nature. On TurboWarp level Blitz 2 plays better than level Difficult on Scratch 3, at 4 seconds think time. - "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, makes many deliberate mistakes - Easy 2: searches 1 ply, makes some deliberate mistakes - Blitz 1: searches 2 plies (4 on TurboWarp) plus subsequent captures / checks - Blitz 2: searches 3 to 4 plies (8 on TurboWarp) plus subsequent captures / checks - Medium: think time 15 seconds for midgame, 10 seconds for endgame (or ply 4 reached); searches ca. 5 plies plus all subsequent capture (+ check) sequences during midgame, more checks during endgame - Difficult: think time 25 seconds for midgame, 15 seconds for endgame (or ply 5 reached); searches ca. 6 plies plus all subsequent capture (+ check) sequences during midgame, more checks during endgame. FIDE ELO rating ca. 1750 on Scratch 3, ca. 2150 on TurboWarp and a fast system. - Difficult (competition mode, press 'c'): think time 90 seconds; searches ca. 8 plies plus all subsequent capture (some check) sequences during midgame, more checks during endgame The fast TurboWarp runtime will add ca. 4-5 plies on Medium and Difficult, and doubles the plies on Blitz 1+2. Press 'c' to toggle 60 seconds think time on Difficult Press 'd' for debugging info (evaluation, search depth, NPS, MPS) Press 'p' for profiler mode (Stats, 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 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!
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