For Experienced Solvers
Hard Sudoku Online & Advanced Pencil-Mark Tips
In SudoLoom Hard Sudoku, visual scanning alone (Naked/Hidden Singles) won’t be enough. You will need to combine Notes Mode with pair-elimination strategies.
1. Snyder Notation
Inside each 3×3 box, only pencil-mark a candidate when it has exactly 2 possible cells. This keeps notes clean and reveals Pointing Pairs.
2. Naked Pair & Hidden Pair
When 2 cells in the same row, column, or box share the exact same 2 candidates {a, b}, remove a and b from all other cells in that unit.
3. Smart Auto-Cleanup Notes
Our board automatically removes duplicate candidate notes in the same row, column, and 3×3 box as soon as you place a valid digit.
Want to master Pointing Pairs, X-Wing, and XY-Wing?Explore Solving Strategies Guide →