Privacy & credits
You can play without an account, installation, or cookies.
Simple first-party measurements
We measure page loads, puzzle-number searches and selections, game attempts, whether an incorrect move was tried, hints, retries, solution views, completed puzzles, and whether our Android app link was visible or clicked. We distinguish playing without help, using a hint, and practicing after viewing a solution. We do not record which moves you played.
Events include a puzzle number where relevant, a broad traffic source (such as YouTube), a small/large screen category, visible-page time and a limited loading-error category. Traffic source comes from a recognized link parameter or the referring website's domain; we do not copy its full address into these events.
A random page identifier connects events within one loaded page. It exists only in page memory, is sent with those events, and is not saved in cookies or browser storage. A reload or another page gets a new identifier. We do not use an advertising ID, fingerprint your browser, or recognize returning visitors.
These are approximate page-interaction counts, not unique-person counts or confirmed app installations. Event logs are currently retained for 30 days. Private aggregate reports may be kept longer. Our hosting providers, Google Firebase and Cloud Run, separately process standard connection and security logs, which can include IP addresses.
No third-party analytics or advertising scripts run on this website. We disable our event collection when your browser sends Do Not Track or Global Privacy Control, or when you use this measurement-free entry link. The opt-out is carried through the site's internal puzzle links, not stored as a persistent preference.
The Android app and Google Play have their own privacy information. Contact: the support contact on our Google Play listing.
How puzzles are checked
These are composed positions. The challenge is to force checkmate within the stated number of moves, starting from the displayed FEN. Position history before the question is not part of a repetition claim. Every accepted solver choice is independently checked against all legal defenses within that limit. The site plays one verified defense; faster mates are also accepted.
The server uses python-chess (GPL-3.0-or-later). The chess-piece images are reused from the creator application's existing asset set.