Learn the grid, then find your rhythm.

Your first scan of a puzzle

Begin with a row, column or box that already contains many givens. Ask which digits from 1 to 9 are missing. For each missing digit, check where it is blocked by the same digit in a crossing row or column. If only one cell remains possible, enter the digit.

Then scan by number. Choose one digit—for example, 7—and look at all nine boxes. Existing 7s eliminate rows and columns inside the other boxes. This often reveals a placement that is difficult to see when you examine one cell at a time.

Repeat both scans. A new answer changes its row, column and box, so a quiet area of the grid can become solvable immediately after a placement elsewhere.

When to write candidates

If a cell can accept more than one digit, do not guess. Turn on Notes and write the remaining candidates. To find them, remove every digit already present in the cell's row, column and box. The values left are the only legal possibilities for that cell.

A cell with one remaining candidate is a naked single. A digit that can appear in only one cell of a row, column or box is a hidden single, even if that cell still displays several notes. These two ideas solve most beginner positions and are explained with examples in the singles guide.

Useful game controls

Notes

Notes store small candidate digits in the selected cell. Remove a candidate when a placement in the same row, column or box makes it impossible. Clean notes make patterns easier to recognize.

Hints

A hint can reveal or guide a useful next move. Before using one, perform one complete row scan and one complete number scan. If you use a hint, study why the revealed value is forced rather than treating it as a random answer.

Undo and erase

Undo reverses your latest action. Erase clears an entry or note from the selected cell. Neither control changes a fixed given. Keyboard users can select cells with the arrow keys and enter digits with the number row or numeric keypad.

A repeatable beginner routine

1. Check the most complete rows, columns and boxes for missing digits.
2. Scan one digit across all nine boxes.
3. Fill every naked or hidden single you can prove.
4. Update candidates affected by each new placement.
5. When no single remains, look for a pair or a locked candidate.
6. After every elimination, return to singles before searching for a harder pattern.

This order matters. Advanced techniques usually create a simple placement; they do not replace the basic scan. If you are moving from Easy to Medium, practice the routine slowly and favor accuracy over the timer.

How to recover from a mistake

If an entry is marked wrong, do not immediately try another digit. Check the selected cell's row, column and box, then compare its candidates with every given in those three areas. Use Undo if the incorrect entry changed several notes.

If a board feels impossible after several moves, inspect the earliest uncertain placement. A contradiction usually comes from a guess or an overlooked duplicate, not from needing a more complicated technique. The common Sudoku mistakes guide provides a longer recovery checklist.