Sudoku Solving Techniques: From Naked Singles to the X-Wing
June 17, 2026
A well-made Sudoku never requires a guess. Every digit can be reasoned out from the ones already on the grid — the trick is knowing which technique to reach for. This guide moves from the methods that solve every Easy puzzle up to the patterns you need for a sparse, stubborn Hard grid.
Singles: the foundation
Two simple ideas will carry you through most puzzles:
- Naked single. Look at one empty cell and cross off every digit already present in its row, column, and 3×3 box. If only one digit survives, it belongs there.
- Hidden single. Pick a digit and a unit (a row, column, or box). If there is only one cell in that unit where the digit can legally go, place it — even if that cell could in theory hold other numbers too. Hidden singles are the engine that drives most of your progress.
Scan by digit, not by cell
Beginners stare at one empty cell and ask “what goes here?” Faster solvers pick a digit — say 7 — and sweep the whole board asking “where must the 7s go?” Because each row, column, and box needs exactly one 7, this cross-hatching quickly corners the digit into forced positions. Work the digits that already appear most often first; they have the fewest places left to hide.
Pairs and pointing
When singles dry up, start eliminating candidates:
- Naked pair. If two cells in the same unit can only hold the same two digits, those two digits are locked to that pair. Remove them from every other cell in the unit — often this creates a new single elsewhere.
- Pointing pair. If, within a box, a digit can only appear in cells that all share one row or column, then that digit can be erased from the rest of that row or column outside the box.
Advanced: the X-Wing
The X-Wing is the first “aha” technique most solvers learn for Hard puzzles. Find a digit that, in two different rows, can only appear in the same two columns. Those four cells form a rectangle. Because the digit must occupy opposite corners of that rectangle, it can be eliminated from everywhere else in those two columns. Swordfish is the same idea stretched across three rows and three columns. You will rarely need these on Easy or Medium, but on a sparse Hard grid they are often the move that breaks the deadlock.
Never guess — track instead
If you feel tempted to guess, it almost always means there is an elimination you have not spotted yet. Slow down, pick one digit, and recheck each unit. Because our puzzles are guaranteed to have a single solution, the logic is always there to be found. That guarantee is what separates a fair Sudoku from a frustrating one — and it is why patient technique always beats trial and error.