Sudoku Strategies – Solving Techniques

Level 1 – Beginner Techniques

Naked Single (Last Remaining Candidate)

A Naked Single occurs when, after eliminating all digits already present in the same row, column, and box, only one digit remains as a candidate for a cell. This is the most common technique of all and handles most of an Easy-difficulty puzzle on its own.

How to spot it: Enable the notes mode and pencil in all candidates for every empty cell. Any cell with exactly one candidate is a Naked Single — fill it in right away.

Hidden Single (Last Possible Place)

A Hidden Single occurs when a specific digit can only go in one cell within a row, column, or box — even though that cell itself may appear to have multiple candidates. The digit is "hidden" because the cell still looks open to many options, but the digit is already excluded from every other position in that unit.

Tip: Go through each digit 1–9 and mark where it can still appear in each box. If a digit appears in only one cell of a unit, you have found a Hidden Single.

Level 2 – Intermediate Techniques

Naked Pair

A Naked Pair arises when two cells within the same unit (row, column, or box) both contain exactly the same two candidates and no others. Those two digits must be distributed between those two cells — in some order. Therefore both digits can be eliminated as candidates from every other cell in that unit.

Example: Two cells in a row both have only {4, 7} as candidates. The 4 and 7 in that row belong exclusively in those two cells. Any other cell in the row that lists 4 or 7 as a candidate can have those candidates crossed out.

Hidden Pair

A Hidden Pair occurs when two specific digits appear as candidates in only two cells within a unit. Even though those two cells may have additional candidates, the two digits in question are confined to those two cells. All other candidates in those two cells can therefore be eliminated.

Tip: The Hidden Pair is harder to spot than the Naked Pair. Look at each digit and track which cells in a unit it appears in. If two digits always co-occur in the same two cells, you have a Hidden Pair.

Pointing Pairs / Box-Line Reduction

When a digit within a 3×3 box can only go in cells that all lie in the same row or column, that digit must land somewhere in that row/column inside the box. It can therefore be eliminated from all other cells of that row or column outside the box — and vice versa.

Level 3 – Advanced Techniques

Naked Triple / Quadruple

An extension of the Naked Pair to three (or four) cells: three cells in a unit that together contain only three candidates in any distribution form a Naked Triple. Those three digits are confined to those three cells and can be eliminated from the rest of the unit.

X-Wing

The X-Wing looks at two rows (or two columns): when a specific digit appears as a candidate in only the same two columns across both rows, the digit must land in one of those four intersection cells. Every other occurrence of that digit in those two columns (outside the two rows) can be eliminated.

Swordfish

The Swordfish is the X-Wing extended to three rows and three columns. It appears less often and is considerably harder to spot, but unlocks crucial eliminations in the toughest puzzles.

The In-Game Hint System

Our built-in hint system analyses the current puzzle state and shows you exactly which technique applies next — from Naked Singles up through Hidden Pairs and beyond. Each hint comes with an explanation so you understand the strategy and can apply it yourself in future puzzles. This way you improve step by step without having the entire solution handed to you.