How to Play Sudoku

The Rules

Sudoku is played on a 9×9 grid, divided into nine 3×3 boxes. Fill in the remaining empty cells so that:

• Each row contains 1–9 exactly once
• Each column contains 1–9 exactly once
• Each 3×3 box contains 1–9 exactly once

That's it — three simple rules. No math is involved. Every puzzle can be solved using logic alone, without any guessing.

Solving Techniques

1. Scanning

Start by scanning rows, columns, and boxes for digits that appear frequently. If a number already appears in two rows within a band of three boxes, the third row can only place that number in one remaining box.

2. Pencil Marks (Candidates)

Use pencil marks to note all possible digits for each empty cell. As you fill in numbers, eliminate candidates from related cells. When a cell has only one candidate left, that's the answer.

3. Naked & Hidden Singles

A Naked Single is a cell with only one possible candidate. A Hidden Single is when a digit can only go in one place within a row, column, or box. These two techniques alone can solve most Easy and Medium puzzles.

4. Naked Pairs, Triples & Pointing

When two cells in a row/column/box share the same two candidates, those digits can be eliminated from all other cells in that group. Similar logic extends to triples. Pointing techniques eliminate candidates when a digit in a box is confined to a single row or column.

For a complete guide to all 28 techniques, visit our Learn Sudoku Techniques page.

Game Modes

• Classic Mode — Unlimited puzzles at your chosen difficulty. Play at your own pace.
• Daily Challenge — Three new puzzles every day (Easy, Medium, Hard). Keep your streak alive.
• Tournament — Create or join competitive lobbies. Race through puzzles and earn rating points.
• Duel — 1v1 matches with Elo-style ratings. Same puzzle, same clock — the faster solver wins.
• Training Mode — Practice specific techniques across five difficulty levels. Use the Next Step button for guided, step-by-step solving.

Controls

• Select a Cell — Click/tap any empty cell, or use arrow keys
• Enter a Number — Click a number button or press 1-9
• Pencil Marks — Toggle pencil mode or hold Ctrl while typing
• Erase — Click eraser or press Delete/Backspace
• Undo/Redo — Unlimited undo/redo during play
• Multi-Select — Hold Ctrl and click, or click-drag to select multiple cells

Tips for Beginners

• Start with Easy puzzles and gradually increase difficulty.
• Focus on one 3×3 box at a time — complete the easiest boxes first.
• Look for cells with only one or two possible candidates.
• Use pencil marks generously — they are your most powerful tool on harder puzzles.
• Never guess. Every puzzle has a unique solution reachable by logic alone.
• Use Training Mode's Next Step feature to learn techniques interactively.
• Play Duels to sharpen your speed under pressure.