Hit a wall on your Sudoku grid? Before resorting to guessing, follow this 6-step logical diagnostic checklist with visual examples to find overlooked moves.
Every Sudoku player—from beginner to expert—occasionally hits a wall where no obvious placement appears. Before resorting to random guessing (which almost always leads to a contradiction later), work through this 6-Step Logical Rescue Protocol.
Count how many times each digit (1 through 9) is already placed on the board. Very often, a digit has quietly reached 8 placements without you noticing, meaning the 9th and final instance can be placed immediately!
If scanning where a digit goes ("Hidden Single") yields nothing, inspect empty cells that sit at the intersection of heavily populated rows and columns. Count from 1 to 9 to see which digits are blocked—you will often find a cell where 8 digits are blocked, leaving a Naked Single.
Verify that none of your candidate notes conflict with a digit you placed recently. A single leftover candidate note can hide a Naked Pair or Locked Candidate.
Human eyes naturally group cells by 3×3 boxes. Slowly scan each individual Row (1 to 9) and Column (1 to 9) to see if a missing digit has only one valid cell along that line.
