Naked singles: place the only candidate
A naked single appears when one empty cell has only one legal digit left. You find it by checking the cell against its row, column, and 3×3 box.
Key idea
If a cell has one candidate after all three constraints are checked, place it immediately.
See the move, step by step
Follow R5C5 inside a real puzzle position, from a busy board of notes to a confirmed 5.
Step 1 of 3
Check all three peer groups
Start at R5C5 and scan row 5, column 5, and the center box. The surrounding values eliminate every digit except 5.
Step 2 of 3
Keep the one legal candidate
R5C5 contains just one note: 5. The other open cells remain full of possibilities, but this cell is solved.
Step 3 of 3
Place 5 and scan again
Write 5 at R5C5. The candidates across its row, column, and box update, creating fresh solving opportunities elsewhere on the board.
Try it on today's puzzle
Scan one box at a time. For every empty cell, check row, column, and box before moving to a harder technique.
Play today