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Puzzles and difficulty ratings
Puzzles are generated by software and checked automatically for a single solution. Difficulty levels come from our own logical solver and describe the techniques it needed. They are not an official or universal scale, and the same puzzle might be rated differently elsewhere. Despite these checks, an error is always possible; please report it if a puzzle seems wrong.
Solver results
The Sudoku solver works only with classic 9 × 9 puzzles and only with the clues you enter. A result of no solution or more than one solution usually means a clue was mistyped or left out. The solver cannot check variant puzzles such as killer, jigsaw or diagonal Sudoku.
Hints and guides
Hints explain one logical step from the current grid using the techniques described in our Sudoku tips. If no supported technique applies, the hint says so instead of guessing a reason. The guides are general explanations of Sudoku techniques, not formal teaching material.
No health or educational claims
Sudoku is a pleasant logic puzzle. We do not claim that it improves memory, prevents illness, raises test scores or provides any therapeutic benefit, and nothing on this site is medical, psychological or professional advice.
Children
The 4 × 4 and 6 × 6 grids are designed for younger players and do not ask for personal details to play. We recommend that a parent, guardian or teacher supervises children's internet use, including on this site.
Timers, scores and saved games
Elapsed times, mistakes and completion records are stored only in your browser and are for your own interest. They are not verified, compared with other players or kept by us, and they can be lost if browser data is cleared.
Sponsored content and external links
Sponsored articles, if published, are labelled as sponsored. Their authors are responsible for their claims, and we do not endorse the products or services they mention. External links are provided for convenience; we are not responsible for the content of other websites.
Questions
If anything on this site is unclear or inaccurate, please contact us through the contact page. See also the terms and conditions.