- This is very cool and having stalemate is nice, however how much space would it take to implement the full ruleset?
As you write: not implemented: castling, en passant, promotion, repetition, 50-move rule - those are all required to call the game being played modern chess.
I could see an argument for skipping repetition and 50-move rule for tiny engines, but you do need castling, en pessant and promotion for pretty much any serious play.
https://en.wikipedia.org/wiki/Video_Chess fit in 4k and supported fuller ruleset in 1980 did it not?
So I would ask what is the smallest fully UCI (https://www.chessprogramming.org/UCI) compliant engine available currently?
This would be a fun goal to beat - make something tiny that supports full ruleset.
PS my first chess computer in early 1980s was this: https://www.ismenio.com/chess_fidelity_cc3.html - it also supported castling, en pessant, not sure about 50 move rule.
- Cool project. You could also use the front-end of GNU chess to save some lines, and implement only a back-end.
Bug report:
a b c d e f g h
8 r n b q k b n r 8
7 . . p p p p p p 7
6 . p . . . . . . 6
5 p . . . . . . . 5
4 P . . P P . . . 4
3 . . . . . . . . 3
2 . P P . . P P P 2
1 R N B Q K B N R 1
a b c d e f g h
move: b2b3
ai: b6b4
The pawn is not permitted to move two fields after it has already beeen moved once before: b6b4 isn't a valid move after b7b6. (First moving two fields, and then one would have been okay, in contrast.)
- Cool! I just recently implemented a chess engine in ~400 (readable) lines, with all rules, first in Java and then ported to my own programming language "Bau" [1]. This is including a terminal UI. I'll measure the ELO, but I was never able to beat it :-) The castling moves are specially tricky to implement I think. I enjoyed the challenge as well.
[1] https://github.com/thomasmueller/bau-lang/blob/main/src/test...
- If anyone is curious, the most common tool I've seen for ELO estimation among engine developers is cutechess [1], which uses SPRT [2]. Or ordo [3], haven't used this myself though
[1] https://cutechess.com/
[2] https://www.chessprogramming.org/Sequential_Probability_Rati...
[3] https://github.com/michiguel/Ordo
by lekevicius
2 subcomments
- Do you think it would be possible to achieve 1:1 ELO:bytes? Even smaller, but can be less smart.
- How many games did you have to throw away because stockfish wanted to castle? Or did you force stockfish to not castle? Castling seems like such a frequent move it is hard to draw any conclusions about the strength of an engine that does not support it.
- https://www.chessprogramming.org/Toledo is a family a moderately strong tiny chess programs.
by kachapopopow
0 subcomment
- need to start measuring these things in the size of compiled functions so we can stop looking at oneliners (maybe wasm since it has an easy to read text representation)
- I wonder how big 1300, 1400, ..., 2200 Elo chess engines are.
- Cool that you could keep it under 2k but it would nice to have a readable version of the source code.
Do you work with it like this or do you have some sort of script you apply to get it down to a single line, single letter variable names?
- How did you handle games where Stockfish would castle or promote?
by oh_my_goodness
1 subcomments
- If you ever spent much time at a chess club, you've seen why 2kB is a really disturbing number.
by haute_cuisine
1 subcomments
- This is amazing! Thanks for sharing. What would be the elo gain for 4KB engine?
P.S. I assume 1200 elo in chess com scale (not lichess / fide elo) and bullet chess variant?
by falsaberN1
0 subcomment
- Oh my god the source is so tiny! It's really hard to parse because of it being minified but I love it to bits.
- Good job! I love how you obfuscated your code, really in a spirit of FOSS!
- The mailbox board representation is a good call for size-constrained engines. Bitboards give faster move generation but the manipulation code (shifts, masks, magic numbers for sliding pieces) eats a lot of bytes. With mailbox you just need offset tables and a sentinel check for board edges. Curious what your evaluation function looks like though. At 2KB you can't fit piece-square tables (that's 384 values minimum for both colors), so are you doing material-only eval or did you squeeze in some positional heuristics?
The gap between your 1200 Elo in 2KB and the TCEC 4K engines at ~3000 Elo is interesting. That extra 2KB buys a lot when it goes to better evaluation and move ordering. Even a simple captures-first sort in alpha-beta pruning costs only a few bytes of code but can roughly double your effective search depth.
by raphaelmolly8
0 subcomment
- [dead]
- [dead]
- Codex or Claude Code?
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