Sudoku - Play Free Online | Wipzu
About Sudoku
Sudoku is the world's most popular logic puzzle, solved by hundreds of millions of people every day. The rules fit in one sentence: fill a 9×9 grid so that every row, every column, and every 3×3 box contains the digits 1 through 9 exactly once. No arithmetic is involved — pure logical deduction, and every properly constructed puzzle has exactly one solution.
The puzzle was invented by American architect Howard Garns and first published in 1979 in Dell Pencil Puzzles magazine under the name 'Number Place.' Japanese publisher Maki Kaji introduced it to Japan in 1984 as Sudoku (shortening 'Suji wa dokushin ni kagiru' — the digits must remain single). It stayed largely unknown outside Japan until retired New Zealand judge Wayne Gould spent six years building a computer puzzle generator, then convinced The Times of London to run it in November 2004. Within weeks every major British newspaper had a Sudoku column.
Solving techniques scale directly with difficulty. Easy puzzles are solved with two methods: naked singles (a cell with only one possible remaining digit) and hidden singles (a digit that can go in only one cell within its row, column, or box). Medium puzzles require naked pairs and pointing pairs. Hard puzzles may demand X-Wing patterns — a technique where a candidate appears in exactly two cells in each of two rows, and the four cells form a rectangle whose columns allow all other instances of that candidate to be eliminated.
The mathematical scale of Sudoku is staggering. In 2005, mathematicians Bertram Felgenhauer and Frazer Jarvis calculated the exact number of valid 9×9 grids: 6,670,903,752,021,072,936,960 — approximately 6.67 × 10²¹. When symmetry equivalences are collapsed, roughly 5.47 billion essentially different puzzles remain. Every grid you complete is one unique point in that near-incomprehensible space.
Key Features
- Three difficulty levels (Easy / Medium / Hard) with different numbers of pre-filled starting clues
- Pure logic puzzle — every valid Sudoku has exactly one solution reachable without guessing
- Invented by American Howard Garns in 1979; became a global phenomenon after The Times London published it in November 2004
- 6.67 × 10²¹ valid grid configurations — every puzzle you encounter is one unique arrangement from that space
- Solving techniques range from beginner (naked singles) to advanced (X-Wing, Swordfish) — the game grows with you
- Built in HTML/CSS/JavaScript — instant browser play with a clean distraction-free interface
Controls
How to Play
- 1Choose a difficulty — Easy for a relaxed solve, Hard when you want a real challenge.
- 2Click any blank cell to select it, then press a digit key (1–9) to fill it in. Your goal: every row, column, and 3×3 box must contain 1–9 exactly once with no repeats.
- 3Use elimination: if a row already has 7 of the 9 digits, only 2 remain for the empty cells. Cross-referencing the column and box narrows it to one.
- 4Look for hidden singles: scan each 3×3 box to find a digit that can go in only one cell, even if that cell still has multiple other candidates.
- 5When direct placement stalls, add pencil marks — small candidate numbers in each cell. Look for naked pairs: two cells in the same unit sharing exactly two identical candidates can have those digits eliminated from all other cells in that unit.
- 6Continue filling cells until every row, column, and box contains 1–9 without any repetition.
Tips & Tricks
- Start with the most-constrained unit on the board — the row, column, or box with the most pre-filled digits. More filled cells mean fewer remaining candidates, yielding fast placements and a chain reaction of new constraints.
- Don't add pencil marks early. Work through naked singles and hidden singles by scanning first. Premature marking clutters the grid and slows you down — only write candidates when direct placement has completely stalled.
- Cross-hatch systematically: pick a digit (say, 7) and check which cells in each 3×3 box can receive it based on where 7 already appears in the crossing rows and columns. If only one cell in the box can hold it, place it.
- Update your candidates immediately after every placement. A new digit eliminates itself as a candidate from every cell in the same row, column, and box. Stale pencil marks cause cascading errors on harder puzzles.
- Never guess. A valid Sudoku is always solvable by logic. If you feel forced to guess, there is an elimination technique — often a naked pair, pointing pair, or X-Wing pattern — that you haven't applied yet.
Game Info
FAQ
No. A properly constructed Sudoku is always solvable by logic alone. If you feel stuck and tempted to guess, it means there is an elimination technique — naked pairs, pointing pairs, or a more advanced pattern — that you haven't spotted yet.
American architect Howard Garns invented it in 1979, publishing it as 'Number Place.' Japanese publisher Maki Kaji renamed it Sudoku in 1984. It became a global phenomenon only in 2004 after retired judge Wayne Gould convinced The Times of London to publish it, and it spread from there to every major newspaper worldwide.
Difficulty is set by the number of pre-filled clues. Easy puzzles have more starting digits, meaning fewer candidates per cell and simpler deduction chains. Hard puzzles have fewer clues and require advanced techniques like naked pairs or X-Wing patterns to solve without guessing.
A naked single is a cell with only one possible remaining digit after its row, column, and box are accounted for. A hidden single is a digit that can go in only one cell within a specific row, column, or box — even if that cell has other candidates. Together, these two techniques solve every Easy puzzle.
Exactly 6,670,903,752,021,072,936,960 — approximately 6.67 × 10²¹. This was calculated in 2005 by mathematicians Bertram Felgenhauer and Frazer Jarvis and independently verified. It remains one of the most cited results in combinatorial puzzle mathematics.