Welcome to "Scratch Chess - Game of Kings". FAQs: - "There is a bug!" Unlikely, 310k games, ✔︎ NO KNOWN ISSUES ✔︎. Consult experienced player, read instructions. - "Why invalid move?" It 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 Junior 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 (Medium) resp. 20 seconds midgame / 15 seconds endgame (Difficult)). On Blitz, Easy and Junior levels, response time is 0 to 3 seconds on decent hardware. Scratch is inherently slow due to its design and interpreted nature. - "Castling doesn't work!" It does, see castling rules. - "How to castle?" Move the king two squares; 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? Maybe you observed the king castling? - "Opponent pawn captured my pawn which had already passed it!" That's called 'en-passant', and is a valid move. - "Why is it a draw when engine only has 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): - Junior 1: searches 1 ply plus 3 subsequent captures, makes many mistakes - Junior 2: searches 1 ply plus 3 subsequent captures, makes some mistakes - Easy: searches 1 ply plus 3 subsequent captures / checks - Blitz: searches 2 plies plus all subsequent captures / checks - Medium: think time 10 seconds; searches 3-5 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; searches 4-6 plies plus all subsequent captures / checks during midgame, more during endgame (on fast systems) - Difficult (competition mode, press 'c'): think time 40 seconds; searches 5-7 plies plus all subsequent captures / checks during midgame, more during endgame (on fast systems) The fast TurboWarp runtime will add 3-5 plies on Medium and Difficult. Press 'c' to toggle 40 seconds think time on Difficult Press 'd' for iterative deepening debug info Press 'p' for profiler mode (shows CPU time spent per function and search depth, number of transposition table hits) 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! I focused on playing strength and usability. Considering the speed limitations of Scratch it shouldn't be too bad It usually calculates 4 to 8 moves ahead (max. is 25 moves, only achieved on TurboWarp and during endgame), depending on selected level, board complexity and system speed. Remix instructions: Remix BEFORE playing, otherwise lists will be too large for saving. Or run the "RUN_BEFORE_SAVING" custom block.
