How Weakspot works
What's real, where the puzzles come from, how the weakness map is calculated, and what isn't built yet.
Where the puzzles come from
All puzzles come from the Lichess puzzle database, released under CC0 (public domain). Lichess generates each puzzle from a real game and verifies it with Stockfish; players then rate it. Weakspot keeps 2,530 of them: puzzles with a popularity score of 85 or more, at least 800 plays and a settled rating, up to 84 per theme spread across six rating bands. Each puzzle links to its original page on Lichess. Weakspot is not affiliated with Lichess.
How a puzzle is graded
The opponent makes the first move, then you play the solution. A move is correct if it matches the engine solution, or if it delivers checkmate on the final move (some positions have more than one mate). Every move is checked by a full rules engine in your browser: castling, en passant and promotion all work.
A puzzle counts as solved only if you get it right on the first try without a hint. A wrong move, a hint or "show solution" counts as a miss. You can still finish the puzzle, but the miss stays on your record.
How the weakness map is calculated
Every puzzle carries the Lichess theme tags for the patterns it contains. When you finish a puzzle, each of its pattern tags (fork, pin, back-rank mate and so on; not phase tags like "middlegame") gets one attempt, and a success if you solved it. The map shows first-try accuracy per pattern once you have three or more attempts, sorted weakest first.
Your puzzle rating uses an Elo-style update against each puzzle's Lichess rating. It's a guide for picking puzzles at the right difficulty, not a Lichess or FIDE rating.
How the adaptive drill chooses
About 70% of the time it picks one of your two weakest patterns (accuracy under 85%); otherwise it samples core patterns you haven't tried enough. Within a pattern it picks unseen puzzles within about 250 points of your rating. Pro adds spaced review: a missed puzzle returns after 1 day, then 3, 7 and 21 days after each correct retry.
Where your data lives
Your stats live in your browser's local storage. We don't have an account system or store your puzzle history on a server. If you clear your browser data, your map resets. Pro status is linked to your Stripe customer record and checked against Stripe. See the privacy policy.
What isn't built yet
Importing your own games from Chess.com or Lichess to find the patterns in your real losses is in development. It isn't live, and we don't claim results from it. Pro subscribers get it first at no extra cost.
Who makes this
Weakspot is a small independent project. Text on this site is drafted with AI assistance and reviewed by a person before publishing; the chess content (puzzles and solutions) comes from Lichess's engine-verified database, not from AI. Corrections are welcome at hello@weakspot.app.