Puzzles: a selection of 100,000 combinations from the Lichess open puzzle database, downloaded 14 October 2026. Puzzle data is released under CC0 1.0. We filter for popularity ≥85, at least 1,000 plays, rating 600–2600, 2–5 player moves and at least 10 pieces in the starting position. Each solution is checked for legal moves before inclusion. The library is finite; practice has no daily limit. Unseen positions are prioritized, then positions can be reviewed.
Chess rules: chess.js 1.4.0, copyright Jeff Hlywa and contributors, BSD-2-Clause. License.
Piece artwork: Colin M. L. Burnett (Cburnett), GPL-2.0-or-later, distributed unmodified as SVG source files. Original source · License.
Oversky Chess is an independent project, not affiliated with Chess.com or Lichess. Chess.com was used as a reference for the puzzle-solving experience; its puzzle database, branding and proprietary artwork are not used.