The right sudoku strategy depends on your difficulty level. Every puzzle from beginner to extreme is solvable by logic alone — no guessing required — but the techniques you need change as the difficulty increases. This guide covers all seven core strategies in the order you should learn them. Start here, then play free sudoku at internetsudoku.net to practise each one.

Strategy 1 — Scanning and Elimination

Scanning is the foundation of every sudoku solve. Work through each row, column, and 3×3 box systematically: for each group that already contains many numbers, determine whether any missing digit can go in only one empty cell in that group.

For every empty cell, eliminate all digits already present in its row, column, and box. If only one digit remains after elimination, fill it in. This single pass will solve most beginner puzzles entirely and opens every harder grid.

Strategy 2 — Naked Singles

A naked single occurs when an empty cell has only one possible digit left after you eliminate all digits already present in its row, column, and 3×3 box. It is the most common move in easy and normal sudoku.

To find naked singles efficiently, write all remaining candidates in each empty cell as small pencil marks. Any cell with only one pencil mark is a naked single — fill it in immediately and cross that digit off as a candidate from all other cells in the same row, column, and box. This often reveals further naked singles.

Strategy 3 — Hidden Singles

A hidden single is a digit that can only fit in one cell within a particular row, column, or box — even though that cell has other candidates visible. The digit is "hidden" because the cell does not look like a naked single at first glance.

To find hidden singles, scan through each digit (1–9) in turn. For each digit, check every row, column, and box where it has not yet been placed: can it go in only one empty cell within that group? If yes, fill it in. Hidden singles are frequently the only way to make progress in normal and hard puzzles after naked singles are exhausted.

Strategy 4 — Naked Pairs (and Triples)

A naked pair occurs when exactly two cells in the same group share exactly the same two candidate digits — and no others. Those two digits must go in those two cells in some order, which means they can be safely eliminated from every other cell in that group.

Example: if cells A and B in the same row both show only candidates [3, 7], then 3 and 7 must occupy A and B. You cannot yet determine which is which, but you can eliminate 3 and 7 from every other cell in that row (and from the column and box those cells belong to). This frequently unlocks new naked or hidden singles elsewhere.

A naked triple extends the same logic to three cells sharing exactly three candidates. Look for triples when pairs alone leave you stuck.

Strategy 5 — Pointing Pairs

If a digit can only appear in two or three cells within a 3×3 box, and those cells all lie in the same row or column, the digit can be eliminated from the rest of that row or column outside the box. This is called a pointing pair (or pointing triple).

Example: if the digit 5 can only go in two cells in the top-centre box and both those cells are in row 2, then 5 cannot appear anywhere else in row 2. Eliminating 5 from cells in row 2 outside that box frequently opens hidden singles in adjacent boxes.

Strategy 6 — X-Wing

X-Wing looks across two rows for a pattern involving a single digit. If a digit can only appear in exactly two cells in row A, and exactly two cells in row B, and those four cells share the same two columns, the digit is locked to those four positions. In either diagonal assignment, the digit cannot appear anywhere else in the two columns.

Eliminate that digit from every other cell in both columns. X-Wing is the first strategy that requires looking at two rows and two columns simultaneously, and it only becomes visible once you have a complete, accurate candidate grid. It appears in hard and extreme puzzles.

Strategy 7 — XY-Wing

An XY-Wing involves three cells: a pivot with exactly two candidates [X, Y], and two wing cells — one with candidates [X, Z] and one with [Y, Z]. The pivot sees both wings. Whichever value the pivot takes, one wing is forced to Z. Therefore, any cell that can see both wing cells cannot contain Z — eliminate Z from those cells.

XY-Wing is harder to spot than X-Wing but resolves positions in extreme puzzles where no other technique finds a move. It requires patience and a complete candidate list.

Which Strategies Do You Need by Difficulty?

Difficulty	Strategies Required
Beginner / Easy	Scanning, Naked Singles
Normal	+ Hidden Singles, Naked Pairs
Hard	+ Pointing Pairs
Extreme	+ X-Wing, XY-Wing

Work through the strategies in this order. Each technique rests on the one before it. Practice each level at internetsudoku.net until the technique feels natural before moving up. For a broader introduction, see our sudoku tips guide.

Frequently Asked Questions

What is the best sudoku strategy for beginners?

Start with scanning and naked singles. Scan every row, column, and box for empty cells where only one digit is possible after eliminating the digits already visible in that group. This technique alone solves every beginner puzzle and most easy grids.

What is a hidden single in sudoku?

A hidden single is a digit that can only fit in one cell within a particular row, column, or box, even though that cell shows multiple candidates. Scan for each digit in turn across every group to find them.

Do you ever need to guess in sudoku?

No. Every sudoku puzzle on internetsudoku.net has a unique solution reachable through logic alone. If you feel forced to guess, there is a technique you have not yet spotted. Step back and scan for naked pairs, pointing pairs, or X-Wing patterns before concluding you are stuck.

What is X-Wing in sudoku?

X-Wing is an advanced technique used in hard and extreme puzzles. If a digit can only appear in exactly two cells in each of two different rows, and those cells share the same two columns, the digit can be eliminated from every other cell in those two columns.