How to Play Sudoku

Q: What are the rules of Sudoku?

Fill every row, column, and 3x3 box with the digits 1-9, with no repeats. Each valid Sudoku has exactly one solution, and every puzzle can be solved through logic alone — no guessing required.

Q: What is the difference between easy, medium, and hard Sudoku?

Easy puzzles have more given numbers and can be solved with basic scanning. Medium puzzles require pencil marks and elimination techniques. Hard puzzles demand advanced strategies like naked pairs and hidden singles.

Q: How do I get better at Sudoku?

Practice daily, use pencil marks, and learn to scan the whole grid rather than focusing on individual cells. Start with easy puzzles and work up to harder difficulties as you recognize patterns faster.

Q: What are pencil marks in Sudoku?

Pencil marks are small candidate notations you write in cells to track which numbers are still possible. They help you spot patterns and make deductions, especially in medium and hard puzzles.

Sudoku is a number puzzle played on a 9×9 grid. No math required. You fill in the blanks using logic alone.

The Rules

Every Sudoku grid has 81 cells arranged in 9 rows, 9 columns, and 9 boxes (the 3×3 sub-grids). Some cells already have numbers. Your job: fill in the rest.

Each row must contain the digits 1 through 9, with no repeats.
Each column must contain the digits 1 through 9, with no repeats.
Each 3×3 box must contain the digits 1 through 9, with no repeats.

That's it. One rule, applied three ways. Every valid Sudoku has exactly one solution.

Basic Strategy: Scanning

Start by scanning rows, columns, and boxes for numbers that are already placed. If a row has eight numbers filled in, the missing one is obvious. But even with fewer clues, you can often narrow things down.

Pick a number (say, 5) and scan the entire grid. Look at each 3×3 box that's missing a 5. The existing 5s in crossing rows and columns will eliminate most cells, often leaving just one possibility.

Elimination

For a given empty cell, list every number that could go there by checking its row, column, and box. If only one number remains, that's your answer.

This is called "naked singles" in Sudoku terminology. It's the most fundamental technique, and it'll carry you through most easy puzzles without anything fancier.

Pencil Marks

When scanning and elimination don't immediately solve a cell, write down the candidates. These small notations (called pencil marks) track which numbers are still possible for each cell.

On Sudoku Cove, hit the Pencil button (or press P) to toggle pencil mode. Numbers you enter will appear as small marks in the corner of the cell.

As you place numbers elsewhere, come back and update your pencil marks. Patterns emerge. Two cells in a box that can only hold the same two numbers? That's a "naked pair" — those numbers are locked to those cells, and you can eliminate them from other cells in the box.

Tips for Beginners

Start with easy puzzles. They have more given numbers and require only basic scanning. Try today's easy daily puzzle.
Work the whole grid, not one cell. Jumping around finds more placements than staring at a single empty cell.
Use pencil marks on medium and hard puzzles. Trying to keep candidates in your head is a losing game once there are 40+ empty cells.
Never guess. Every Sudoku can be solved through logic alone. If you're stuck, you're missing a deduction, not a lucky guess.
Practice daily. Pattern recognition improves fast with daily play. The daily puzzle is a good habit.

Ready to play?

Today's Daily Puzzle Free Play