Sudoku
Hint used: today's daily won't count on the leaderboard.
Click a cell, then type 1 to 9. N switches notes, P pauses.Tap a cell, then a number. Notes pencil in candidates.
About the game
Sudoku
Sudoku is a logic puzzle on a 9×9 grid: fill every row, column and 3×3 box with the digits 1 to 9, each exactly once. Every puzzle here has a single solution you can reach without guessing, in four levels from Easy to Expert, plus a daily puzzle.
- Modern form
- 1979, United States
- Named
- 1984, Japan
- Grid
- 9 × 9, digits 1 to 9
- Levels here
- Easy to Expert, Daily
How to play
The board is a 9×9 grid split into nine 3×3 boxes. Fill every empty square with a digit from 1 to 9 so that each row, each column and each 3×3 box contains every digit exactly once. The starting digits cannot be changed. Every puzzle here has exactly one solution and can be solved by logic, without guessing.
- Enter a digit: select a square, then tap a number on the pad or press 1–9.
- Notes: turn on Notes (or press N) to pencil in candidates. Shift+digit adds a note without switching modes.
- Move: arrow keys. Erase: Delete. Undo: Ctrl+Z. Pause: P.
- Mistakes: a digit that does not match the solution turns red and is counted. There is no limit.
- Hint: fills the selected square, or the most constrained empty square if none is selected.
Levels
- Easy: 36 or more starting digits; singles only.
- Medium: about 30 starting digits; singles only, harder to spot.
- Hard: needs pointing pairs and naked or hidden pairs.
- Expert: needs techniques beyond pairs, such as X-Wing.
- Daily: one Medium puzzle per day, the same for every player.
Strategy
- Naked single. If eight digits already appear in a square’s row, column and box, the ninth goes there.
- Hidden single. Within one row, column or box, a digit that fits in only one square goes there, even if that square has other candidates.
- Pointing pair. If a digit’s candidates inside a box all lie in one row, remove that digit from the rest of the row outside the box. Columns work the same way.
- Naked pair. Two squares in a unit with the same two candidates own those digits; remove them from every other square in the unit.
- Hidden pair. Two digits that fit only in the same two squares of a unit; clear every other candidate from those squares.
- X-Wing. A digit that, in two rows, fits only in the same two columns sits on opposite corners of that rectangle; remove it from the rest of both columns.
Origins
The grid comes from an American puzzle. Howard Garns, a retired architect from Indiana, created the modern form, and Dell Magazines published it in 1979 as Number Place. Similar ideas had appeared much earlier: in 1892 the French newspaper Le Siècle printed a partly filled 9×9 magic square with 3×3 subsquares.
The name is Japanese. In April 1984 the publisher Nikoli introduced the puzzle in Japan under a title meaning “the digits must be single”, soon shortened to Sudoku. Nikoli set the conventions still used today: a limited number of givens and symmetrical layouts.
History
- 1892 Le Siècle in Paris prints a partly completed 9×9 magic square with 3×3 boxes.
- 1979 Dell Magazines publishes Howard Garns’s Number Place.
- 1984 Nikoli brings it to Japan and gives it the name Sudoku.
- 1986 Nikoli limits the givens to 32 and makes the patterns symmetrical.
- 2004 A New Hampshire paper prints it in September; The Times of London starts on 12 November and the craze spreads worldwide.
- 2014 Researchers publish a proof that 17 is the fewest clues a sudoku with one solution can have.
- 2026 This version on Zippi, with a daily puzzle and a world leaderboard.
Why it’s fun
- Every step is certain. A good puzzle never needs a guess, so each digit you place is proof, not luck.
- Progress snowballs. Each digit removes options elsewhere, so a slow start turns into a fast finish.
- The rules fit in one sentence. Anyone can start; the depth comes from technique, not from more rules.
- A clean finish. A full grid with no mistakes is one of the most satisfying endings in puzzles.
What it trains
Sudoku is practice in logical deduction, keeping several constraints in mind at once, and working carefully: one wrong digit spreads, so checking before you commit becomes a habit.
FAQ
How does the daily leaderboard work?
Choose Daily to play the same Medium puzzle as everyone else that day. Our server times you from your first move until you solve it, so pausing or leaving the tab does not stop the leaderboard clock. Using a hint takes that day’s puzzle off the leaderboard. You can add a name; no account is needed.
Does every puzzle have one solution?
Yes. Each puzzle is checked for a single solution before it is shown.
Are my best times saved?
Your best time for each level is kept on this device and shown when you solve a puzzle.
This version
- A new puzzle every game, each checked for exactly one solution and graded by the techniques it needs.
- Daily puzzle with a world leaderboard timed by our server.
- Notes, hints, undo, mistake count and a number pad that shows how many of each digit are left.
- The puzzle, notes and timer are saved on this device; the timer pauses when you switch tabs.
Updates
- New colours: slate grid, blue highlights for the selected square, its row, column and box, and matching digits.
- Daily puzzle and world leaderboard for the fastest times.
- First version on Zippi: four levels, notes, hints and undo.
Page last reviewed .
