Sudoku
Play Sudoku — easy through expert, no mid-game popups.
Classic Sudoku — a 9×9 grid split into nine 3×3 boxes. Fill every blank cell with a digit 1–9 so each row, each column, and each 3×3 box contains every digit exactly once. No arithmetic, no diagonals — just those three constraints. Every puzzle has a unique solution, so you never need to guess. Progress saves locally.
Part of: Daily Challenges
Before you judge the score
Treat the score as feedback on one short practice round. It may reflect speed, attention, memory, or familiarity with the format, not overall ability.
The best next step is to review one missed pattern or one slow decision, then try a related practice or guide.
Cognitive Boost fit
Use Sudoku as a Spatial Attention warm-up
Sudoku is not arithmetic. It is scanning, constraints, and patience. Use it before a Spatial Attention run when you want a slower visual-logic reset.
- Grid Scan: Sudoku supports scanning, candidate checking, and attention to position.
- Speed vs. Accuracy Check: A repeatable Sudoku move can show whether slowing down improves accuracy.
More about this tool
How to use this tool
- The rules: fill every blank cell with 1–9 so that each of the 9 rows, 9 columns, and nine 3×3 boxes contains every digit exactly once.
- A digit is legal in a cell only if it doesn't already appear in that cell's row, column, or 3×3 box.
- Tap a blank cell to select it; press 1–9 (or tap the number buttons) to place a digit. Backspace/Delete/0 clears.
- Red highlighting means you broke a rule — undo and rescan. A proper Sudoku is always solvable by logic alone; if you feel like guessing, you missed a deduction.
- Starter technique: pick a digit like 1, scan all nine 3×3 boxes, and place it in any box where only one cell can legally hold it. Repeat for 2 through 9, then loop back — each placement opens new forced moves.
- Pick a difficulty at the top; your progress auto-saves per difficulty.
Examples
Next up
Frequently asked questions
› Is there math in Sudoku? Trust & accuracy
No. The digits 1–9 are symbols — you could replace them with letters or shapes and the game would be identical. No addition, no multiplication.
› Do diagonals count?
Not in standard Sudoku. Only rows, columns, and 3×3 boxes have the once-each-digit rule. "Diagonal Sudoku" is a variant, not the default.
› Can I take notes? Trust & accuracy
Pencil marks are planned for a future version. For now, use mental candidates or scratch paper on hard puzzles.
› Why does a cell highlight red? Troubleshooting
Your digit violates one of the three rules — same digit already in the row, column, or 3×3 box.
› How is the board generated? How-to
Backtracking solver fills a full 9×9, then removes cells while verifying uniqueness — every puzzle has exactly one solution.
Tips & related reading
See the Daily Challenges hub →Tips & how-tos
- Sudoku Difficulty Explained
- Beginner Sudoku Strategy
- The 15 Best Free Word Games on Kefiw
- Sudoku Rules: How to Play
- How to Solve Sudoku Faster
- How Daily Sudoku Builds Logical Reasoning
- Sudoku Beginner Tips: Common Stuck Points
- Sudoku Difficulty Levels Explained
- A Daily Brain-Health Routine After 40
- Brain Games for Seniors That Stay Fun Enough to Keep Doing