Sudoku technique guide

Hidden Single Sudoku Technique

A hidden single is a number that has only one possible place in a row, column or box. This guide explains the idea in plain English, when to look for it, and the common mistake to avoid.

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At a glance

Difficulty

Beginner

This is where Hidden Single normally sits in a human solving path.

Family

Basic Sudoku techniques

It belongs to the basic sudoku techniques group of Sudoku logic.

Main action

Usually remove candidates

Most technique moves reduce notes first. That often reveals a simpler placement afterwards.

What is Hidden Single?

A hidden single is a number that has only one possible place in a row, column or box.

The important thing is that this is logic, not guessing. You are using the current candidates to prove that a number must either go in one place, or cannot stay in another place.

In SudoSketch, this technique is designed to work with notes and Coach highlighting, so the key cells and removal cells can be shown clearly.

How Hidden Single works

Pick one row, column or 3x3 box.
Choose one candidate and check every place it could go.
If the candidate fits in only one cell, place it there even if that cell has other notes.

When to look for it

Look for Hidden Single after easier moves have stopped working. First check for naked singles, hidden singles, locked candidates and simple pairs. If those do not move the puzzle forward, this technique may be worth checking.

For learning, do not try to scan for every advanced technique at once. Pick one method, understand the shape, and practise spotting that one pattern.

Common mistake

Do not confuse a hidden single with an empty-looking cell. The number must have only one possible place in the chosen area.

If you are unsure, rebuild the candidates first. Bad notes create bad logic, and Sudoku will absolutely punish you for it like a tiny spreadsheet goblin.

Hidden Single FAQ

What is Hidden Single in Sudoku?