Sudoku — Classic Number Puzzle
Play Sudoku in your browser. Three difficulty levels, mistake tracking, timer, and a built-in solver.
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Frequently asked questions
How do I enter numbers and pencil marks?
Is my game progress saved?
What is the best strategy for beginners?
Did Sudoku really originate in Japan?
How do I know if I have made a mistake?
What are the three difficulty levels?
What are pencil marks and how do I use them?
Is the game accessible for players with disabilities?
What is the world record time for solving a Sudoku?
How many valid Sudoku puzzles are there?
About Sudoku — Classic Number Puzzle
Sudoku is the world's most popular logic puzzle, appearing daily in newspapers across more than 100 countries and played by an estimated 100 million people worldwide. Despite its Japanese name — which translates roughly as "single numbers" (a shortening of "Suuji wa dokushin ni kagiru," meaning the digits must remain single) — the modern Sudoku puzzle was not invented in Japan. Its direct predecessor was "Number Place," designed by American architect Howard Garns and first published in Dell Pencil Puzzles and Word Games magazine in 1979. Japanese publisher Nikoli discovered the puzzle, refined its rules, and trademarked the name Sudoku in 1984. British newspaper The Times introduced it to Western audiences in 2004, triggering a global craze that made it a fixture of daily life within months.
The rules are beautifully simple. The puzzle presents a 9×9 grid divided into nine 3×3 boxes. Some cells are pre-filled with digits from 1 to 9; the rest are blank. Your task is to fill every empty cell so that each row, each column, and each 3×3 box contains every digit from 1 to 9 exactly once. A well-constructed Sudoku puzzle has exactly one valid solution, and it can always be reached through logical deduction alone — no guessing is required. Click a cell to select it, then tap a number on the on-screen pad or press a keyboard key to fill it in.
Sudoku strategy builds in layers of complexity. Beginners start with "naked singles" — cells where only one digit can legally go based on what already appears in the same row, column, and box. A related technique, "hidden singles," identifies rows, columns, or boxes where a particular digit can fit in only one position even if that cell has multiple candidates. Intermediate players use pencil-marking: noting small candidate digits in the corner of empty cells to track possibilities. From there, techniques like naked pairs, pointing pairs, and X-wings allow elimination of candidates without guessing. This browser version supports pencil marks natively — press the pencil icon or hold Shift while entering a number to toggle candidate mode.
Beyond technique, Sudoku rewards a calm, systematic mindset. Expert players rarely need to guess; instead they scan methodically for constraint violations and apply solving techniques in order of complexity. This browser version generates a fresh, guaranteed-solvable puzzle every time with three difficulty settings. Easy puzzles have approximately 35 empty cells and rely on naked and hidden singles alone. Medium introduces more complex eliminations. Hard puzzles have around 55 empty cells and may require intermediate techniques. A running timer, mistake counter, and built-in solver make it ideal for players of all levels — from first-timers to seasoned enthusiasts chasing their best times.
Sudoku: An American Invention That Japan Gave to the World
Howard Garns was a 74-year-old retired architect living in Indiana when he invented Number Place in 1979. Dell Magazines published his puzzle in their pencil puzzle book, tucked among crosswords and word searches, where it attracted a modest but loyal following. Garns died in 1989, never knowing what his creation would become. It was Maki Kaji, the founder of Japanese puzzle publisher Nikoli, who found the puzzle in a Dell magazine around 1984, saw its potential, gave it the name Sudoku, and began publishing it in Japan. Nikoli added the aesthetic rule that the given clue cells must be arranged with 180-degree rotational symmetry — a design constraint that made the puzzles feel more elegant and is still followed by most publishers today.
For two decades Sudoku was largely a Japanese phenomenon, beloved but unknown outside puzzle enthusiast circles. That changed in 2004 when Wayne Gould, a retired Hong Kong judge and computer programmer, brought a handwritten Sudoku book back from Japan and spent six years writing a computer program to generate puzzles. He gave the software to The Times of London for free in exchange for a byline. The Times published its first Sudoku on 12 November 2004, and within weeks every major British newspaper had launched its own daily puzzle. The craze crossed to the United States, continental Europe, and Australia by 2005. Sudoku books outsold almost every other category at bookshops in the UK during the Christmas season of 2005.
The puzzle's spread coincided with an unexpected scientific controversy. In 2012, Irish mathematician Gary McGuire published a proof claiming that the minimum number of clues required to produce a Sudoku puzzle with a unique solution is 17. His team used a computational search taking over seven million core-hours to verify that no valid 16-clue puzzle exists. The result was later independently confirmed. This means every Sudoku puzzle you encounter in newspapers and puzzle books — and every one generated by this tool — contains at least 17 pre-filled cells, even when they feel almost empty.