How Mated Verifies Chess Puzzles
A complete forced-mate proof before play, then a bounded tree check when you submit.
A complete forced-mate proof before play, then a bounded tree check when you submit.
Mated screens candidate positions before scheduling them. The supplied move sequence must replay legally from its board state and end in checkmate. The pipeline derives mate depth from the moves rather than trusting a label, applies quality and difficulty floors, and rejects malformed moves, unsupported depths, duplicates, and underpromotions the live board cannot reproduce.
Every selected position retains internal provenance for audit and licensing checks. Mated does not publish that record as an outbound play destination. If a license ever requires attribution, the public page must provide it.
The same production chess engine used in the browser runs offline before a Daily puzzle is committed. A mate-in-N candidate passes only when the engine proves a forced mate in N moves and also proves there is no faster mate in N minus 1.
A candidate that fails either proof, exceeds the proof-time budget during selection, or cannot be regenerated exactly during release verification does not ship.
At each attacking turn, the generator finds every legal move that preserves the required forced mate. After each accepted move, it records every legal defensive reply and recursively proves the continuation until checkmate.
The result is a complete branching forced-mate tree, not one preferred principal variation. Alternate first moves and later winning choices remain accepted, while a single saving defense is enough to disqualify a line.
The oracle has strict node and file-size limits so Daily validation stays bounded. If a complete tree exceeds those limits, Mated rejects the entire candidate and selects another position.
Mated never makes an oversized position fit by deleting defensive branches or alternate winning moves. That rejection rule is what keeps the promise that every verified winning line counts.
The browser receives the FEN, a standard text description of the board and side to move, plus the mate depth, difficulty band, and day number. The public position and bundled engine are enough for a determined player to calculate the answer. Mated does not pretend the chess position is secret.
The acceptable-move tree, internal source reference, and node count stay in the committed server document. They are withheld to keep the browser payload small and the public data clean, not because the solution is a cryptographic secret.
When a player submits a Daily solve, the server validates the UCI move format and a move-list limit tied to the published mate depth. It then walks the committed tree, checking both the attacking move and the actual defensive reply at every branch.
The solve is accepted only when the final submitted move reaches a stored mate leaf. PHP does not run a second chess engine during the request; it performs a small deterministic membership check against the proof built before publication.
Daily verification protects the shared streak, result, rewards, and leaderboard. Public learning examples are zero-write study positions. Mastery and Rush progress are intentionally client-attested and remain isolated from authoritative Daily competition.
Being explicit about those boundaries is part of verification: Mated claims server-authenticated results where that proof exists and does not imply the same trust model for lower-stakes practice.
Yes. The FEN describes the complete board and side to move, and Mated ships a browser chess engine. The server oracle authenticates a submitted Daily line; it is not an attempt to hide a calculable chess answer.
A forced-mate position can have more than one winning move or continuation. Mated records every move that preserves the required mate and every legal defensive reply, so an alternate verified line is accepted.
No. The production chess engine proves the complete tree offline. The PHP server checks the submitted move sequence against that committed tree and accepts it only when the sequence ends on a stored mate leaf.
Mated rejects the entire candidate and selects another position. It does not remove alternate wins or defensive branches merely to make the oracle smaller.
Mated is a 21x20 Media game. The rest of our daily games are at 21x20.com.