Sudoku is a placement puzzle, not an arithmetic test. The symbols happen to be digits, but you never add or multiply them. You use the same nine symbols to satisfy three overlapping sets of constraints.
How do you play Sudoku?
Fill the 9×9 grid so every row, every column and every 3×3 box contains the digits 1 through 9 exactly once. Start from the printed givens, find which digits are missing from a unit, and eliminate cells blocked by crossing rows, columns and boxes. Place a digit only when one value or one position is forced.
What are the rules of Sudoku?
A standard Sudoku has 81 cells arranged in nine rows, nine columns and nine 3×3 boxes. Some digits are printed at the start; these are givens and cannot be changed. Empty cells must be filled with digits 1–9.
The phrase “exactly once” is important. A row cannot repeat a digit, a column cannot repeat it, and a box cannot repeat it. When the puzzle is complete, each unit contains the full set 1–9. A legal move must satisfy all three units containing that cell.
Do you need to be good at math?
No. Digits act as nine distinct labels. Classic Sudoku uses no calculation; the work is constraint checking and elimination. If the symbols were nine letters, the underlying puzzle would be the same.
How do you find the first move?
Choose a row, column or box with many givens. List its missing digits. For each missing digit, use the crossing units to eliminate impossible cells. If a digit has only one position left in the unit, place it.
Another useful scan follows one digit across the grid. If two boxes in a horizontal band already contain 7, their rows may block positions in the third box and leave one cell for 7. Repeat this cross-hatching scan for digits 1 through 9.
What is a naked single?
A naked single is a cell with one legal value. If its row, column and box already contain every digit except 4, the cell must be 4.
What is a hidden single?
A hidden single is a digit with one possible position inside a unit. The winning cell may show several candidate notes, but the digit appears nowhere else in that row, column or box.
When should you use candidate notes?
Add candidates when direct scanning stops producing placements. Write every digit that remains legal in an unresolved cell. Notes are a map of current possibilities, not guesses. Remove a candidate whenever a new placement appears in the same row, column or box.
Candidate notes reveal pairs, triples and box-line interactions. Keep them complete: a missing legal candidate can create a fake pattern, while an obsolete candidate can hide a real single.
What mistakes should a new Sudoku player avoid?
- Checking only the row: every cell also belongs to a column and box.
- Choosing a plausible digit: legal does not mean forced.
- Keeping stale notes: update candidates after every placement.
- Staring at one region: switch between digits, rows, columns and boxes.
- Revealing an unexplained answer: ask for the technique or region first.
A reliable beginner loop is scan, place, update and restart. The restart matters because one digit often creates a new single elsewhere.
Free tool / Paper-ready
Want to test the rule on your own puzzle?
Take or upload a clear Sudoku photo, review every recognized given, and choose one hint or the full solution. The editable transcription matters: correct any faint or misread digit before asking the solver to reason from the grid.
Open the Sudoku Solver from Photo →About our game: Detective Sudoku applies one-per-row-and-column deduction to suspects, rooms and truthful clues. It is not classic Sudoku, and its real hints explain a clue-driven deduction instead of giving away the answer or solution.
Frequently asked questions about playing Sudoku
What is the object of Sudoku?
Complete the grid so each row, column and 3×3 box contains digits 1–9 once, with no repeats.
Can Sudoku have two of the same number in a row?
No. A repeated digit in any row, column or box violates the standard rules.
Should a beginner guess in Sudoku?
No. Record candidates and place a digit only when a constraint forces the value or its position.
What should you learn after singles?
Learn locked candidates and naked pairs, then return to singles after every elimination.