Lesson 1 · Start here
Sudoku Rules
Learn the three rules that make every valid Sudoku move possible.
See the logic move
Use Next to reveal each reason. On the final step, tap the highlighted cell to complete the move yourself.
Step 1 of 3
Check across
The target cell is in row 5. Scan every number already in that row.
What the board is showing
FocusStart here. This is the cell or area being investigated.R5C5
Relevant cellsThese cells share the row, column, or box used by this step.Row 5
Explain it simply
Your job is to place 1 to 9 so no number repeats in a row, column, or 3x3 box.
Step by step
- Check the row.
- Check the column.
- Check the 3x3 box.
- Place the number only when all three allow it.
Quick check: Can a number appear twice in one 3x3 box if it is in different rows?
No. Every 3x3 box must contain each number only once.
Turn logic into skill