Methodology
Puzzles come from two sources: positions mined from the project's own engine self-play games in all 960 starting setups, and — for classical chess — the open Lichess puzzle database (CC0).
How every puzzle is verified
Each candidate is replayed by Stockfish at depth 20 or deeper: the solution line is played out against the engine's best replies, and the position is rejected unless the winning idea is forced.
Puzzles that pass get a verified mark, an engine evaluation with search depth, a human-readable name and a link to their starting position. Rejected candidates never ship.