🔢 How to Play Sudoku
Sudoku is a logic-based number placement puzzle played on a 9×9 grid divided into nine 3×3 boxes. The grid starts partially filled. Your task is to fill every empty cell with a digit from 1 to 9 so that each row, each column, and each 3×3 box contains every digit exactly once — with no repeats. You cannot change the pre-filled clue numbers.
Click any empty cell to select it (highlighted in blue), then click a number on the number pad or press a digit key to enter it. Use the Hint button (3 available per game) to reveal the correct digit in your selected cell. Check validates your entire current board. Three difficulty levels control how many clues are given: Beginner (40 clues), Intermediate (30 clues), Advanced (25 clues).
Tips & Strategies
- Single candidate: If only one digit can legally go in a cell (all others appear in the same row, column, or box), place it immediately.
- Single position: If a digit can only appear in one cell within a row, column, or box, place it there.
- Scan rows and columns for digits 1–9 in turn — locate where each must go by elimination.
- Use the highlight feature: clicking a cell highlights its row, column, and 3×3 box to see conflicts at a glance.
- Never guess. Every valid Sudoku has a unique solution reachable by pure logic.
History & Background
Number puzzles similar to Sudoku appeared in French newspapers in the 1890s. The modern 9×9 form was developed by architect Howard Garns in 1979 and published as Number Place. Japanese publisher Nikoli popularised it as "Sudoku" in 1986, and it went worldwide after The Times (London) began publishing it in 2004. Today billions of Sudoku puzzles are solved every year.