Garf/stoofvlees-data

Stoofvlees Training Data

Chess training data produced for Stoofvlees, winner of the 2023 World Computer Chess Championship (Valencia) and 2024 (Santiago de Compostela).

This dataset corresponds to the training data described in:

Pascutto, G. (2025). Sin Dolor No Hay Gloria: On Conquering 2 World Computer Chess Championships in Spain. ICGA Journal, 47(3), 136–156. https://doi.org/10.1177/13896911251360654

Dataset contents

File(s)	Size	Contents
train_fullgame.zdat (+.idx)	~356 MB	Games played to completion, without early adjudication/resignation
train_fullgame1.zdat (+.idx)	~3.9 GB	Games played to completion, without early adjudication/resignation
train_all.zdat (+.idx)	~109 GB	Training data
train_early.zdat (+.idx)	~120 GB	Training data
test80-2024-{mar,apr,may,jun,jul,aug,sep}.zdat (+.idx)	~72–176 GB each	Leela Chess Zero training data, converted to this format for data-mix experiments

Positions are subsampled rather than exhaustive; long endgames and drawn games are under-represented relative to their share of full games.

File format

.zdat / .zdat.idx

.zdat files hold variable-length zstd-compressed groups of fixed-size position records, compressed against a shared dictionary embedded in the file. .zdat.idx is a companion index giving byte offsets for random access.

• .zdat header: magic SJNGDAT1 (8 bytes) + entry_size (u32) + batch (u32, records per group) + level (u32, zstd compression level) + dict_len (u32) + a zstd dictionary blob of dict_len bytes, followed by a sequence of zstd frames — one frame per group of batch positions, each frame compressed against the dictionary.
• .zdat.idx header: magic SJNGIDX1 (8 bytes) + record count (u64) + count + 1 absolute byte offsets (u64 each) into the corresponding .zdat file — offset i is the start of frame i, offset count is the end of the file.

Per-position record (uncompressed, decoded from each .zdat group)

Each record is a fixed 4545-byte struct, <368s4096B18fffB in Python struct notation:

Field	Size	Description
bitplanes	368 bytes	46 bit-packed 8×8 boards, 1 byte per row, MSB-first files a–h. Always oriented from the side-to-move's perspective (board flipped if black to move). See layout below.
policy	4096 bytes	MCTS visit-count policy target, one byte per (from, to) move (index = from_square * 64 + to_square). 0 = illegal move; otherwise the value is 1 + round(p * 254) for policy probability p (decode: p = (value - 1) / 254).
scalars	18 × float32 (72 bytes)	Auxiliary position/game-state features. See layout below.
score	float32	Search/eval score for the position.
outcome	float32	Final game outcome from the position's side to move: -1 (loss), 0 (draw), +1 (win).
moves_to_go	uint8	Plies remaining until game end, clamped to 255. 0 means unknown/not recorded.

Total: 368 + 4096 + 72 + 4 + 4 + 1 = 4545 bytes.

Bitplane layout (planes 0–45)

Planes	Content
0–5	Own pawns, knights, bishops, rooks, queens, king
6–11	Opponent pawns, knights, bishops, rooks, queens, king
12–21	Attack maps for both sides across piece types
22–27	Reserved / engine-internal
28	Open files
29	Own half-open files
30	Own passed pawns
31–33	Reserved / engine-internal
34	Opponent half-open files
35	Opponent passed pawns
36–38	Reserved / engine-internal
39–43	Reserved / engine-internal
44	En passant target square (all-zero if none)
45	Light/dark square color mask (constant, not side-relative)

Scalar layout (scalars 0–17)

Index	Content
0	Static evaluation score, converted from centipawns to a win-probability-style value and rescaled to [-1, 1]
1	Quiescence-search score, converted the same way
2–5	Castling rights: own kingside, own queenside, opponent kingside, opponent queenside
6	Position has occurred before this game (repetition flag)
7	Fifty-move-rule counter, normalized to [0, 1]
8–17	Reserved / engine-internal

License

• train_fullgame.zdat, train_fullgame1.zdat, train_all.zdat, train_early.zdat: CC-BY-4.0
• test80-2024-*: ODbL 1.0 / DbCL 1.0 (converted from Leela Chess Zero training data, provided for ease of use when experimenting with data mixing)

Citation

@article{pascutto2025sindolor,
  author  = {Pascutto, Gian-Carlo},
  title   = {Sin Dolor No Hay Gloria: On Conquering 2 World Computer Chess Championships in Spain},
  journal = {ICGA Journal},
  volume  = {47},
  number  = {3},
  pages   = {136--156},
  year    = {2025},
  doi     = {10.1177/13896911251360654}
}