The Basic Rule
A Sudoku board is a 9 by 9 grid. Fill every empty cell with a number from 1 to 9. Each row, each column, and each 3 by 3 box must contain the numbers 1 through 9 without repeating a number.
- Rows run left to right.
- Columns run top to bottom.
- Boxes are the nine smaller 3 by 3 regions.
Useful Solving Habits
Start with the most constrained areas. If a row, column, or box already has many numbers, it is often easier to find the missing value. Scan for one number at a time, then switch to cells that have only a few possible candidates.
Notes are useful when a cell has two or three reasonable options. Good notes should reduce uncertainty, not fill every cell with every possible number.
Common Mistakes
The most common mistake is placing a number because it fits one row while forgetting the column or box. Before entering a number, check all three regions. In timed or duel play, clean confirmation is usually faster than correcting a rushed mistake later.
When the board feels stuck, return to basics: scan rows, columns, and boxes for missing numbers, then look for cells with a single possible value.