Sudoku technique guide

Nice Loop Sudoku Technique

A Nice Loop is a closed chain of logical links that proves a placement or elimination. 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

Advanced

This is where Nice Loop normally sits in a human solving path.

Family

Visual chain techniques

It belongs to the visual chain 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 Nice Loop?

A Nice Loop is a closed chain of logical links that proves a placement or elimination.

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 Nice Loop works

Follow a closed chain of candidate links.
The chain alternates logical pressure around the loop.
A contradiction or repeated endpoint proves a safe placement or elimination.

When to look for it

Look for Nice Loop 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

Nice Loops are powerful but easy to overread. The loop links must be valid all the way around.

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.

Nice Loop FAQ

What is Nice Loop in Sudoku?