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What is Sudoku?

Sudoku is the world's most popular logic number puzzle. You're given a 9×9 grid partly filled with digits, and your job is to complete it so that every row, every column and every 3×3 box contains the numbers 1 to 9 exactly once. Despite the numbers, Sudoku takes no arithmetic and no special maths skills — the digits are just symbols, and everything you need is logic, patience and concentration.

The modern puzzle was popularised in Japan, and its name is short for a phrase meaning "the digits must be single." It has since become a daily habit for millions of people. Because solving relies on pure deduction, Sudoku makes an excellent brain game: play a puzzle or two each day and you'll notice sharper focus and quicker pattern-spotting over time. Every puzzle on vygam is generated fresh with a single, guaranteed solution, so you can always reach the answer through reasoning alone — never guesswork.

How to Play

A move is a mistake whenever it repeats a digit inside a unit. Specifically, a placement is incorrect if:

• any row ends up with the same number from 1 to 9 more than once;
• any column ends up with the same number from 1 to 9 more than once;
• any 3×3 box ends up with the same number from 1 to 9 more than once.

Sudoku Tips & Strategy

Sudoku is easy once it clicks, but the first few puzzles can feel intimidating. These beginner-friendly techniques will get you solving faster.

1. Start where the grid is fullest

   Scan for any row, column or 3×3 box that already holds five or more numbers. With so few blanks left, the missing digits are the most constrained — often only one number can legally fit a cell once you account for everything already in its row, column and box.

2. Hunt for the missing third

   Split the board into three bands of three boxes. When two boxes in a band already contain the same digit, the third box must hold it too. Cross-reference the rows and columns those digits occupy and you can usually pin the number to a single empty cell.

3. Use pencil notes for candidates

   When a cell could take more than one value, switch on Notes and jot down every candidate. As you fill neighbouring cells, candidates get eliminated — and a cell left with just one note is a guaranteed answer.

4. Never guess

   Every vygam puzzle has exactly one solution reachable by logic, so if you're tempted to guess, there's a deduction you haven't spotted yet. Step back, rescan the tightest unit, and the forced move will appear.

Sudoku Difficulty Levels

vygam offers five difficulty levels so the challenge can grow with you. Easy starts with forty given numbers, leaving plenty of anchors to reason from — ideal for learning the rules or a relaxed coffee-break game. Medium trims the clues to thirty-two, so you lean on scanning and pencil notes a little more often. Hard drops to twenty-eight givens and rewards patient cross-referencing between rows, columns and boxes.

Expert leaves just twenty-five numbers on the board, and its next move is often hidden behind a short chain of deductions. Evil, our toughest tier, begins with only twenty-three clues and demands the sharpest logic you have. Every puzzle at every level is still generated with exactly one solution, so persistence always pays off — there is never a need to guess. Your fastest completion is saved separately for each level, so you can chase a personal best on Easy while slowly working your way up to Evil.

Hints, Undo & Pencil Notes

Stuck on a grid? Tap Hint to reveal the correct digit for a single empty square. Select a cell first to reveal that exact one, or let the game pick an open square for you. Revealed cells are locked in and marked with a small dot, so they are always treated as correct and never count against your mistakes. A hint counter tracks how many you have used, which is handy if you like to finish with as few as possible.

Made a slip? The Undo button steps back through your moves one at a time, restoring the previous value, any pencil notes and the mistake count exactly as they were. It works for placed digits, erased cells and note edits alike, yet it never touches the puzzle's original given numbers. Together with Notes, which let you pencil in every candidate for a cell, these tools make it comfortable to experiment and reason your way to the finish.

The number pad also shows how many of each digit are still left to place — nine minus however many copies you have already placed correctly. When all nine copies of a number are on the board, its key dims automatically, giving you an at-a-glance read of exactly what still remains.

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