Beginner Sudoku Techniques

Sudoku becomes easier when you stop guessing and start looking for information the grid already provides. The aim is to place the digits 1 through 9 once in every row, column, and 3×3 box. Each placement should follow from those three constraints.

Begin with a complete scan

Before writing anything, scan every row, column, and box. Look first at areas that already contain six or more numbers. A crowded area gives you fewer possibilities and usually produces the first safe move. After every placement, scan again because one new digit can unlock several nearby cells.

Naked singles

A naked single appears when an empty cell can accept only one digit. Check the cell's row, its column, and its 3×3 box. Cross out every digit already present. If only one candidate remains, that value is forced. Beginners often miss singles because they inspect only the row; all three regions must be checked.

Hidden singles

Sometimes a cell appears to have several candidates, but one particular digit can occur nowhere else in its row, column, or box. That digit is a hidden single. Choose one missing digit and test each empty position in the region. Existing copies of that digit in crossing rows and columns eliminate positions until only one remains.

Cross-hatching a 3×3 box

Pick a digit and look across the three rows that pass through a box. If that digit already appears in two of those rows elsewhere, the remaining copy inside the box must lie in the third row. Repeat the same process vertically with columns. Cross-hatching is especially effective near the beginning of Easy and Normal puzzles.

Use pencil candidates sparingly

You do not need to write every possible candidate immediately. Start with cells that have two possibilities or with a nearly complete region. Too many notes create visual noise. If you do record candidates on paper, keep them small and erase candidates whenever a digit is placed in the same row, column, or box.

A repeatable solving routine

1. Scan rows, columns, and boxes for missing digits.
2. Fill all naked singles.
3. Search each region for hidden singles.
4. Cross-hatch one digit at a time from 1 through 9.
5. After every placement, return to the most crowded regions.

Avoid guessing

Guessing may appear faster, but one wrong assumption can contaminate the entire grid. If you feel stuck, move to another region or recheck candidates. Stealthdoku keeps an incorrect number red until it is corrected, making the immediate issue clear without ending the game.

Practice suggestion: use Easy puzzles to make scanning automatic. Move to Normal when you can identify singles without checking every digit one by one.