Editorial policy

How puzzles are made

The puzzles here are produced by generator programs rather than assembled by hand. That makes the important question not who wrote a puzzle, but who proved it works. Every puzzle published on the site has been shown to have exactly one solution.

The independent check

A generator is never allowed to approve its own output. For each puzzle type there are two separate programs. One produces candidate puzzles. A second, written against a different algorithm, attempts to prove that each candidate has a single solution. A puzzle is published only when the second program agrees, and a batch that produces a disagreement is discarded rather than shipped.

The separation matters because a program that checks its own work tends to repeat its own mistakes, including the ones that make a puzzle unsolvable. Two independent implementations reaching the same answer is a much stronger signal.

How difficulty is decided

Practice Library puzzles carry five levels, from Easy to Einstein. The level is set by which solving techniques a logical solver actually needs, not by how many cells were removed. Einstein is the strict tier: those puzzles are solvable by deduction from start to finish, so being stuck means a move has been missed rather than that a guess is required.

The Daily puzzles use a separate one to ten grade, with the daily band running from three on Monday to seven on Sunday. Those grades are calibrated against how long a typical player actually takes, not against how intricate a puzzle looks on paper. When players reported that weekday grids were running to twenty minutes, the grading rules were rewritten and the affected puzzles regenerated.

Published puzzles do not change

Once a puzzle has been served it is frozen. Daily puzzles are not edited after their date, archived days replay exactly as they were first published, and completed solves and streaks are never invalidated by a later change. New puzzles are added; existing ones are left alone.

How articles are written

The strategy guides and explainers are written to be checked against the games on this site. When an article describes a technique, it is a technique the solver programs here actually use, and worked examples come from real boards rather than being invented for the page.

Articles carry a publication date and an updated date when they change. Claims about research, such as the effects of puzzles on memory or focus, are written as what the evidence suggests rather than as settled fact.

Corrections

Errors are corrected rather than quietly removed. If you find a puzzle that appears unsolvable, a solution that looks wrong, or a mistake in an article, report it through the contact page or the feedback button on any page. Reports about broken puzzles are prioritised, because a faulty puzzle usually indicates a generator bug that would affect other players too.

Editorial independence

The site is funded by advertising. Advertisers have no influence over what is written, no influence over which puzzles are published, and no ability to buy a mention. Nothing on the site is sponsored content. If that ever changes, the affected pages will say so clearly.