Sudoku
Play the classic number puzzle game with multiple difficulty levels.
How to Use
- Choose a difficulty.
- Fill the grid so each row, column, and 3x3 box contains digits 1-9.
- Use hints if you get stuck.
Frequently Asked Questions
Can I save my progress?
Progress is saved automatically in your browser's local storage.
Sudoku Solver and Strategy Guide: Solve Puzzles Like a Pro
Sudoku rewards logic, not math. This guide covers beginner scanning through advanced techniques like X-Wing and Swordfish for serious solvers.
Sudoku Is Logic, Not Math
Despite using numbers, Sudoku requires no arithmetic. It is a pure constraint-satisfaction puzzle. You fill a 9x9 grid so each row, column, and 3x3 box contains the digits 1 through 9 exactly once. The numbers are merely symbols.
Basic Scanning and Cross-Hatching
Start by scanning rows and columns within each box. If a box already contains a 5, look at the intersecting rows and columns to eliminate where else that 5 can go. This cross-hatching reveals the only valid cell.
Pencil Marking
Write small candidate numbers in empty cells. This externalizes your working memory and prevents you from rechecking the same constraints repeatedly. It is the single most effective habit for intermediate players.
Hidden Singles and Naked Pairs
A hidden single is the only place a number can go in a row, box, or column, even if the cell has other candidates. A naked pair occurs when two cells in a unit contain the same two candidates, eliminating those numbers from other cells in that unit.
Intermediate Techniques
Pointing pairs extend naked pair logic across boxes. Box-line reduction occurs when a candidate in a box is confined to one row or column, allowing you to eliminate it from the rest of that line.
Advanced Patterns
X-Wing finds a candidate that appears exactly twice in two rows, aligned in the same two columns. This eliminates that candidate elsewhere in those columns. Swordfish is the three-row version. These patterns unlock expert puzzles.
Using a Sudoku Solver for Learning
When you are stuck, a solver can show the next logical step rather than the full answer. Study why that step works. Over time, you will recognize the pattern organically.
Building Stamina
Pattern recognition improves with volume. Solve one puzzle daily rather than bingeing ten in a weekend. Consistency trains your brain to see constraints faster.
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Related Tools
- Reaction Time Test — Measure your reflexes by clicking as fast as possible when the signal appears.
- Click Speed Test — Test how many times you can click in 5, 10, or 60 seconds.
- Memory Cards — Match pairs of cards by flipping them. Test and improve your memory.