The dataset

Every position on Fischer Rating, published as open structured data. Each record carries the FEN, the forced solution line, and the same engine-measured facets the rankings are built on — so the numbers behind "best" are open to inspection, never hidden behind a single score. Free to use with attribution.

Field reference

id

Stable identifier for the position.

url

Canonical page for the position on Fischer Rating.

fen

The position in Forsyth–Edwards Notation (Chess960-valid).

side_to_move

Which side is to move and wins — white or black.

solution_uci

The forced solution line, in UCI coordinate moves.

motif

The headline tactical motif (e.g. mate-in-2, fork, sacrifice).

themes

Every tactical theme present in the position.

rating

Difficulty estimate; higher is harder.

key_move

The piece that makes the first, critical move.

sac

Net material sacrificed on the forcing line, in points.

mate_in

Moves to forced mate, or empty when the win is not a mate.

quiet

True when the key move gives neither check nor capture.

fork

True when a single move attacks two or more targets.

line_len

Length of the forced line, in plies (half-moves).

effect

The engine evaluation swing the tactic produces.

rankings

The ranked lists this position appears in, by slug.