Sudoku for beginners: one rule is enough
No arithmetic and no guessing. Once you understand rows, columns and boxes, you are ready.
Three views of the same rule
Every row, column and 3×3 box needs 1–9 exactly once. These three diagrams show the same nearly completed 9×9 teaching grid; only the highlighted region changes. The question mark is the one empty cell.
Row
Column
Box
What belongs in the question-mark cell?
Check the reasoning
9. The row is missing 9, and neither the column nor the box already contains it. All three constraints agree. This deliberately nearly completed teaching grid shows the rule, not the difficulty of a typical starting puzzle. Given numbers stay fixed; diagonals do not need 1–9 in classic Sudoku.
Try your first move on a smaller board
This 4×4 example uses 1–4 and 2×2 boxes. The logic is the same as classic Sudoku; there are just fewer cells to check.
| 3 | 4 | ||
| 3 | ? | 2 | |
| 4 | 2 | ||
| 1 |
Fill every row, column and 2×2 box with 1, 2, 3 and 4, each exactly once. Starting numbers cannot be changed. No arithmetic or guessing is needed.
What goes in row 2, column 3 — the cell marked “?”?
Show the explanation
R2C3 = 1. Row 2 needs 1 or 4. Column 3 already has 3 and 2, and the top-right box has 4, so R2C3 is 1.
What are you trying to do?
A standard Sudoku is a 9×9 grid divided into nine 3×3 boxes. Fill the empty cells so every row, column and box contains the digits 1 through 9 exactly once.
The printed digits are clues and cannot be changed. A well-formed puzzle has one unique solution.
Look before you place
Start with a row, column or box that already contains many digits. Find what is missing, then use the crossing constraints to rule out impossible cells.
- Track one digit at a time
- Begin in the most crowded areas
- Write candidates instead of guessing
A reliable first routine
Scan boxes, then rows, then columns. Each placement creates new restrictions, so repeat the cycle. The puzzle opens one certain step at a time.
Try a row with two empty cells
Suppose a row reads 5, 3, _, 6, 7, 8, 9, 1, _. The missing digits are 2 and 4. That tells us the possibilities, but not their order. If the third column already contains a 4 elsewhere, the third cell cannot be 4: it must be 2. The last cell is then 4, provided its column and box allow it.
This is a local example, not a complete puzzle. Always check all three regions before entering a digit. Being absent from a row alone does not make a number correct.
Use the classic Sudoku controls to practice
Select an empty cell and use the number keys or the on-screen keypad. Notes stores candidate digits; it does not commit an answer. Undo reverses your last move. A hint can flag an incorrect entry, explain a single, or offer to reveal a value when no supported logical step is found. You decide whether to apply it.
For a first session, choose Easy and ignore the timer. Before each entry, say why every other digit is excluded. If you cannot explain a move, leave a note and inspect another region. Game progress is saved in this browser; a different device will not share it.