Common Sudoku Mistakes and How to Avoid Them
Checking only a row
A digit that is missing from a row may still be forbidden by its column or 3 × 3 box. Always examine all three constraints before placing a number.
Treating a note as a confirmed digit
Pencil candidates are possibilities, not answers. Keep them visually separate from filled cells. Eliminate candidates gradually rather than turning an uncertain note into a final answer.
Guessing before scanning
A random guess can cause several mistakes later, making it hard to find the original error. Look for naked singles, hidden singles and pairs before trying advanced approaches.
Rushing the final cells
Near the end, check the three Sudoku rules again. The optional Check button can highlight incorrect entries, but using it adds five seconds. You can also pause the game while taking a break.
Losing your progress
Your puzzle is saved locally on the device you are using. Keep the browser’s site data if you want to continue later; clearing site data or switching devices without synchronization can remove that progress.