Strategy
Sudoku solving techniques
Each technique below has its own guide with a real position taken from a puzzle, and a link that opens that position in the step-by-step solver.
There are twelve techniques you need for almost every Sudoku: naked and hidden singles, naked and hidden pairs, pointing pairs, box-line reduction, naked and hidden triples, X-Wing, Swordfish, XY-Wing and simple coloring. Learn them in this order.
The twelve techniques, in order
Level 1: singles (Easy)
- Naked single: a cell with only one candidate.
- Hidden single: a digit with only one place in a unit.
Level 2: pairs and lines (Medium)
- Naked pair: two cells sharing the same two candidates.
- Hidden pair: two digits that fit in only two cells.
- Pointing pair: a digit in a box confined to one line.
- Box-line reduction: a digit in a line confined to one box.
Level 3: triples (Hard)
- Naked triple: three cells sharing three candidates.
- Hidden triple: three digits that fit in only three cells.
Level 4: fish (Expert)
- X-Wing: a digit locked into two columns across two rows.
- Swordfish: the same across three rows and three columns.
Level 5: chains (Extreme)
- XY-Wing: three cells with two candidates each, in a chain.
- Simple coloring: following a digit through strong links.
How to learn them
- Read one technique guide and study the real example.
- Play a puzzle at the matching level (Easy, Medium, Hard, Expert, Extreme).
- When you get stuck, use the solver in step-by-step mode to see the technique on your own puzzle.
Techniques beyond these twelve
Sudoku has many more patterns, such as XYZ-Wing, unique rectangles and long chains. Our puzzles are verified to be solvable using only the twelve above, so they are all you need here. If you want to go further, the glossary is a good place to start.
Frequently asked questions
What are the Sudoku solving techniques?
Singles, pairs, pointing pairs, box-line reduction, triples, X-Wing, Swordfish, XY-Wing and coloring are the main ones.
In which order should I learn them?
In the order listed above, which follows the difficulty levels.
Which technique is the most important?
Hidden single. It solves most Easy puzzles by itself and is the base of many harder techniques.
Do I need all of them?
For Easy and Medium, no. For Expert and Extreme, yes.