Naked Single

Interactive Tutorial

A Naked Single is the simplest and most fundamental Sudoku solving technique. It occurs when a cell has only one remaining candidate — meaning only one digit can possibly go in that cell.

How It Works

When you eliminate candidates from a cell through the basic Sudoku rules (each digit appears exactly once in every row, column, and box), sometimes you're left with just one possibility. That's a Naked Single.

Example

Look at cell R5C6. What candidates can it have?

• Row 5 already contains 2, 3, 5, 6, 7, 9
• Column 6 already contains 4 and 8
• Box 5 adds no new eliminations

Together, these units eliminate 2, 3, 4, 5, 6, 7, 8, 9 — leaving only 1 as the sole candidate. That's a Naked Single.

puzzle: S9B041F1F102S2S0I03085U0C024I0I04011U3M5U0I05036R370204360C0743064L094I0L040E020I4B4B0J0F070C06430D074L034I090L0I05070T1P08031H1H434Z03093P3P045H1X02044Z0Z0C1V0G5F09
mode: guided
technique: Naked Single
initial:
  layers:
    hints: true
steps:
  - text: >
      Look at R5C6. Row 5 has 2, 3, 5, 6, 7, 9. Column 6 has 4, 8. Only 1 remains.
    hint: subtle
    technique: NS
    state:
      selection:
        cell: R5C6
  - text: >
      Since 1 is the only candidate, it must be the solution for this cell.
    hint: detailed
    technique: NS

When to Use It

Naked Singles should be your first check when scanning the puzzle. They're:

• Easy to spot when candidates are displayed
• Always safe to place immediately
• The foundation for more advanced techniques

Tips

1. Enable auto-candidates in settings to see all possibilities at a glance
2. Use Focus Mode to highlight cells with few candidates
3. After placing any digit, check for new Naked Singles in the affected row, column, and box

More Puzzles

• Naked Single ex. 1

Related Techniques

• Hidden Single — When a digit can only go in one cell within a unit