How to Play Sudoku — Rules & Solving Basics
The Grid
- 9×9 grid = 81 cells
- Divided into 9 rows (horizontal), 9 columns (vertical), 9 3×3 boxes (regions/blocks)
- Some cells pre-filled ("givens") — typically 17-30
The Only Three Rules
- Each row must contain digits 1-9 exactly once
- Each column must contain digits 1-9 exactly once
- Each 3×3 box must contain digits 1-9 exactly once
That's it. No math. Pure logic. Every valid puzzle has exactly ONE solution.
Basic Solving Techniques
1. Scanning (Naked Singles)
Find a cell where only ONE digit fits. Row, column, and box constraints eliminate 8 digits.
2. Cross-Hatching
Focus on ONE digit. Scan rows/columns to find which box MUST contain it. Place it.
3. Pencil Marks (Candidates)
Write possible digits in empty cells. Update as you solve. Digital apps do this automatically.
4. Hidden Singles
A digit can go in multiple cells in a unit, but only ONE cell in the *entire grid* can take it.
5. Naked Pairs/Triples
Two cells in a unit share the SAME two candidates → those digits can't be elsewhere in that unit.
6. Pointing Pairs / Box-Line Reduction
If a digit in a box is locked to one row/column, remove it from that row/column outside the box.
Solving Workflow
- Scan for Naked Singles (easiest wins)
- Cross-hatch each digit 1-9
- Add pencil marks for stuck areas
- Find Hidden Singles
- Spot Naked Pairs/Triples
- Apply Pointing Pairs
- Repeat until solved
- Advanced: X-Wing, Swordfish, XY-Wing, Coloring, Forcing Chains
Common Beginner Mistakes
- Guessing — never needed for valid puzzles
- Ignoring pencil marks — they reveal patterns
- Focusing only on rows — boxes and columns equally important
- Erasing instead of marking — track eliminations
Practice Progression
- Easy: Naked Singles + Cross-Hatching only
- Medium: + Hidden Singles + Naked Pairs
- Hard: + Pointing Pairs + X-Wing
- Expert: + Swordfish, XY-Wing, Chains
- Diabolical: Multiple advanced techniques, minimal givens
Start with "Easy" on any app/site. The logic clicks suddenly — that's the addiction!
