What is Sudoku?
Sudoku is a logic-based number placement puzzle that has captivated millions of players worldwide since it gained international popularity in the early 2000s. The puzzle consists of a 9×9 grid divided into nine 3×3 boxes. The objective is to fill the grid so that every row, every column, and every 3×3 box contains the digits 1 through 9 exactly once. Despite its simple rules, Sudoku offers endless variety and depth — from gentle puzzles that take minutes to fiendishly difficult ones that can take hours. Our free online version features four difficulty levels, pencil marks for notes, hints when you get stuck, and a clean interface optimized for desktop, tablet, and mobile play.
Tips & Strategies
Start by scanning rows, columns, and boxes to find cells with only one possible number — these are called "naked singles" and are the easiest to fill. Use pencil marks to track candidates in each cell, and as you place numbers, eliminate those candidates from related cells. Look for "hidden singles" — numbers that can only go in one cell within a row, column, or box. For harder puzzles, apply advanced techniques like pointing pairs, box-line reduction, and X-Wing patterns. Work systematically: start with the most constrained rows and columns. If you get stuck, take a break and come back with fresh eyes — sometimes the solution becomes obvious after a short pause.
History of Sudoku
Sudoku as we know it today was popularized in its modern form by the Japanese puzzle company Nikoli in the 1980s, who gave it the name "Sudoku" (short for suuji wa dokushin ni kagiru — "the digits must remain single"). However, the puzzle has earlier roots. Number placement puzzles similar to Sudoku appeared in French newspapers in the late 19th century. The modern version was designed by American architect Howard Garns in 1979 and published by Dell Magazines under the name "Number Place". It was introduced to Japan by Nikoli in 1984 and became a global phenomenon in 2004-2005 when British newspapers like The Times began publishing daily puzzles. Today, Sudoku is one of the most popular logic puzzles in the world, enjoyed by millions across all ages and cultures.
How to Play Sudoku
The rules of Sudoku are simple. You are given a 9×9 grid with some cells already filled in. Your goal is to fill every empty cell with a number from 1 to 9. Each number can only appear once in each row, once in each column, and once in each 3×3 box. Click or tap a cell to select it, then type a number or use the number pad below the grid. Use the Notes mode to pencil in candidate numbers in a cell — this helps you keep track of possibilities as you work through the puzzle. If you get stuck, use the Hint button to reveal one correct cell. The Undo button lets you revert your last move. You can pause the game at any time and resume later.
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