Naked Single

Difficulty level: easy

A naked single is a cell where eight of the nine possible numbers are already ruled out by its row, column, and 3×3 box. Whatever number remains is the only legal entry — no guessing involved.

Naked singles are the bread and butter of easy puzzles, and they cascade: placing one often creates the next. Strong players scan for them constantly, because each one placed makes the whole grid simpler.

To rule numbers out, look at all twenty peers of a cell: the eight other cells in its row, the eight in its column, and the four remaining cells of its box. Every value that already appears among those peers is impossible for the cell.

Worked example

How to apply it

1. Pick an empty cell, ideally in a crowded row, column, or box.
2. List the numbers 1–9 and strike out every value visible in the cell's row, column, and box.
3. If exactly one value survives, write it in — it is forced.
4. Re-scan the cell's row, column, and box: your placement may have created new naked singles.

Practice it

The fastest way to internalize the naked single is to use it. Play a free easy puzzle — the in-game hint system points out exactly this pattern when it appears, or browse the full technique library.