GAMESHUSH GAME GUIDES
Sudoku: find a reason for every digit
A good Sudoku move is a conclusion, not a guess. Start with the rule that every row, column and 3 × 3 box contains 1–9 exactly once, then narrow one empty cell at a time.
A first move you can explain
Given clues cannot be changed. Suppose this row has just one empty cell:
5 3 4 | 6 7 8 | 9 1 ·
After entering 2, inspect its column and box again. One confirmed value can remove a candidate elsewhere. Look for nearly complete units before examining the entire board.
Turn possibilities into a deduction
A cell with one candidate
For an empty cell, cross out every digit already used in its row, column and box. If only 7 remains, that cell is 7. This is a naked single. Notes are useful when two or more candidates remain.
A digit with one possible home
Imagine a row missing 2, 5 and 8. After checking the columns and boxes, its three empty cells have these candidates:
| Cell | Candidates |
|---|---|
| A | 2, 5 |
| B | 2, 5, 8 |
| C | 2, 5 |
A pair that clears space elsewhere
Suppose exactly two empty cells in the same row each have only {2, 5}. Those two cells must share 2 and 5 in some order. Remove 2 and 5 from the other cells in that row. A third cell with {2, 5, 8} becomes 8. This naked-pair rule requires exactly two cells restricted to the same two digits; merely seeing a 2 and a 5 among larger candidate lists is not enough.
When a box points along a row
If every possible place for 6 inside one 3 × 3 box lies in the same row, that box’s 6 must be in that row. Remove 6 from the rest of the row outside the box. You still cannot choose which cell in the box is 6 until another clue settles it. This is a locked candidate.
Use the tools deliberately
- Notes: toggle pencil marks in an empty cell. Notes are not automatically pruned after other moves; revisit them after each deduction.
- Undo: reverses board edits, including notes. It does not erase the hint count.
- Hint: reveals a correct digit, prioritizing your selected editable cell when it needs correction. Try to explain the revealed value before continuing.
- Duplicate feedback: flags repeated digits in a row, column or box. A wrong digit can be conflict-free now and cause trouble later.
Select a cell and tap a digit, or use arrow keys and 1–9. N toggles Notes; Backspace, Delete or 0 erases; Ctrl/⌘ Z undoes while a cell is focused. Pause hides the board. Help pauses the timer.
A reliable solving rhythm
- Scan rows, columns and boxes with few gaps.
- Record candidates only after checking all three units.
- Look for singles; then pairs and locked candidates.
- After a placement, update affected notes instead of carrying old assumptions forward.
- If stuck, undo a doubtful entry or use a hint. Faster guessing is not the same as better reasoning.
Questions before your next puzzle
What do the difficulty labels mean?
Easy uses singles. Medium permits locked candidates and naked pairs. Hard may need deeper search. The displayed technique category describes what the solver used; a Medium or Hard puzzle may still be solvable using singles. Every generated puzzle has one solution.
Will my puzzle survive closing the tab?
When browser storage is available, the puzzle, notes, recent undo history, time and settings save locally. Reopening restores it paused. A new puzzle replaces the old one after confirmation. Clearing site data removes progress; it does not sync across devices.