What is Sudoku?
Sudoku is a logic-based puzzle where you fill a 9×9 grid with digits 1-9 so that each row, column, and 3×3 box contains each digit exactly once.
Sudoku is a logic-based puzzle where you fill a 9×9 grid with digits 1-9 so that each row, column, and 3×3 box contains each digit exactly once.
Loved worldwide as a brain-training exercise that sharpens logical thinking.
History of Sudoku
The roots of Sudoku go back to the "Latin Square" concept devised by the 18th-century mathematician Leonhard Euler. The modern puzzle was first published in 1979 as "Number Place" by American architect Howard Garns in a puzzle magazine.
In 1984, the Japanese puzzle company Nikoli introduced it as "Sudoku" (abbreviated from "Sūji wa dokushin ni kagiru" — "the digits must be single"), sparking a huge craze in Japan.
In 2004, British newspapers began publishing Sudoku, leading to a worldwide explosion. Today it is enjoyed in newspapers, apps, and every form of media across the globe.
Rules
Each column contains digits 1-9 exactly once
Each row contains digits 1-9 exactly once
Each 3×3 box contains digits 1-9 exactly once
Pre-filled cells cannot be changed
Select Difficulty
Beginner
Perfect for beginners. Learn the rules while you play.
Easy
Simple logic puzzles for new players.
Medium
Requires a bit more complex thinking.
Hard
Advanced techniques needed to solve.
Expert
For experts. Requires X-Wing and other advanced techniques.
Master
The ultimate challenge. Test the limits of logical reasoning.
Solving Techniques
Sudoku Dojo's hint system automatically detects the following techniques. The harder the difficulty, the more advanced the techniques required.
A cell with only one candidate remaining. The most basic technique.
A digit that can only go in one specific cell within its row, column, or box.
Two cells in the same row, column, or box share the same two candidates. Other cells in that unit can exclude those digits.
When a digit in a box appears only in one row (or column), it can be eliminated from that row (or column) in other boxes.
When a digit in a row (or column) appears only in one box, it can be eliminated from that box's other rows (or columns).
A candidate forms a rectangular pattern across two rows and two columns. Eliminations can be made in other rows and columns.
An advanced extension of X-Wing to three rows and three columns. For experienced players.
A candidate appears in the same row across two columns, creating cross eliminations. A variation of X-Wing.
A regular X-Wing pattern with one extra candidate (the fin). Reasoning proceeds by analyzing whether the fin is valid.
Understanding the difference between hidden and naked pairs.
Solving Tips
- 1
Start by filling in cells with only one possible number. Look for rows, columns, or boxes where a digit can only go in one place.
- 2
Use the notes feature to write candidate numbers in each cell. Narrowing down candidates helps you find the next move.
- 3
Look for "hidden singles" — when a digit can only go in one specific cell within a row, column, or box.
- 4
When two cells in a row, column, or box have the same two candidates, other cells in that unit can't contain those digits.
Frequently Asked Questions
Which difficulty should I start with?
If you're new to Sudoku, start with Beginner. As you gain confidence, gradually increase the difficulty. Each level requires more advanced techniques.
What happens when I make a mistake?
Three mistakes end the game. Incorrect cells are highlighted in red but the error clears when you enter the correct number.
When does the timer stop?
The timer runs until you complete the puzzle or the game ends. Your progress is auto-saved when you close the page.
Does every Sudoku have only one solution?
Yes. All puzzles on this site are algorithmically verified to have a unique solution. Every puzzle can be solved through logical deduction alone — no guessing required.
How do I get a high score?
Scores are primarily based on clear time. Bonus points for no mistakes and no hints used. Take on the daily challenge to compete!