Lichess puzzle database, updated September 10, 2026; first 5,000 rows retrieved September 21, 2026. Database exports: CC0 1.0. Source: https://database.lichess.org/#puzzles . Ratings and themes are a frozen source snapshot, not verified difficulty or coaching claims. Derived FEN and SAN validated with chess.js 1.4.0, BSD-2-Clause. Original artwork and interface required.