Learn them in this order
The techniques below are ranked by what they cost you in effort, which is also the order the site's own solver tries them in. Learn the first two and you can finish any easy puzzle. Add locked candidates for medium, pairs and triples for hard, and the wings and fish for expert.
| Technique | You will need it for | What it does |
|---|---|---|
| Naked singles | Easy | One cell, one possible digit |
| Hidden singles | Easy | One digit, one possible cell in a unit |
| Pointing pairs | Medium | A digit trapped on one line inside a box |
| Naked pairs | Hard | Two cells that own two digits between them |
| Hidden pairs | Hard | Two digits that fit in only two cells |
| X-Wing | Expert | A digit boxed into a rectangle |
| XY-Wing | Expert | Three linked cells that force one digit out |
| Swordfish | Expert | An X-Wing across three lines instead of two |
How to actually learn one
Reading about a technique rarely makes it stick. Play a puzzle at the difficulty where it appears, and when you get stuck press the hint button — it names the technique it used and explains the elimination on the position in front of you. Two or three of those and you will start seeing the pattern before the button does.
Every example on these pages was mined from a real generated puzzle by the same solver that grades the site's difficulty levels. If a diagram says a technique applies, it applies.
Common questions
Which Sudoku technique should I learn first?
Hidden singles. They are the most common move in every puzzle from easy to expert, and they need no pencil marks.
How many techniques do I actually need?
Two will finish easy puzzles, four will finish hard ones. The advanced patterns only matter at expert level.
Do I need to learn chains and colouring?
Not for this site. Every published puzzle can be solved with the eight techniques listed here, which is checked during generation.