Sudoku Rules & Strategies
Master fundamentals and learn logical techniques to tackle harder puzzles efficiently.
- Each row must contain digits 1–9 without repeats.
- Each column must contain digits 1–9 without repeats.
- Each 3×3 box must contain digits 1–9 without repeats.
- Given numbers (clues) cannot be changed.
- The puzzle should have a single unique solution. In SudokuSocial, generation enforces uniqueness and validity.
Use pencil marks (candidates) to note possible digits for an empty cell given row/column/box constraints. As you place digits, eliminate those candidates from peer cells. Our Note mode and Auto-notes automate this process.
Scanning
Check rows, columns, and boxes for obvious placements by elimination.
Naked Singles
Cells with only one candidate.
Hidden Singles
A digit appears only once as a candidate in a unit (row/column/box), so it must go there.
Naked Pairs/Triples
Two/three cells in a unit share exactly the same candidates; eliminate them from other cells in that unit.
Hidden Pairs/Triples
A pair/triple of digits can only appear in a pair/triple of cells in a unit; other candidates in those cells can be removed.
Pointing Pairs/Triples
If a candidate is restricted to a single row/column within a box, remove it from the same row/column outside the box.
Box-Line Reduction
If a candidate is confined to a row/column within a box, remove it from other cells of that row/column outside the box.
X-Wing (overview)
If a candidate forms a rectangle aligned across two rows and columns, eliminate that candidate from other cells in those columns/rows.
Swordfish (overview)
Generalizes X-Wing to three rows/columns.
Coloring/Chains (overview)
Use inference chains to eliminate candidates without guessing.
We plan to add step-by-step interactive hints for these techniques in a future update.
- Start with Easy puzzles; focus on singles and scanning.
- Move to Medium when you solve Easy consistently under 10 minutes.
- Practice Pairs/Triples on Hard puzzles.
- Try Expert after mastering intermediate eliminations.
Tip: Use Note mode and Auto-notes to keep candidates up to date.