Sudoku Strategies
Every sudoku is solvable by logic alone — never guessing. These guides walk through the techniques that get you there, from the scanning any beginner can do to the chains experts rely on. Because form9 uses nine shapes instead of numbers, the logic is laid bare: no arithmetic to distract you, just pattern and deduction. Every method here works exactly the same in ordinary number sudoku.
The only rule you need
Fill the grid so that each row, each column, and each 3×3 box contains all nine shapes exactly once. That's it. Every technique below is just a faster way of asking the same question: given what's already placed, where must this shape go — or what must go in this cell?
Easy techniques
These three methods solve almost every beginner puzzle without any candidate bookkeeping. Learn them in order:
- Beginner Tips & Simple PatternsThe one rule, how to scan rows, columns and boxes, and how to spot a cell that only one shape can fill.
- Naked SinglesWhen a cell has just one candidate left because its row, column and box already hold the other eight shapes.
- Hidden SinglesWhen a shape can legally go in only one cell of a row, column or box — even if that cell could hold others.
New to the game entirely? The easy techniques index collects all three with a one-line summary of each.
Medium & hard techniques
Once singles stop cracking the grid, you move to techniques that eliminate candidates rather than placing shapes directly — locked candidates, naked and hidden pairs, X-Wings and beyond. The medium tier is ready now; hard-tier guides are on the way.
- Medium techniquesNaked and hidden pairs, pointing pairs, box/line reduction, and naked and hidden triples.
- Hard techniques — coming soonX-Wing, Swordfish, XY-Wing and colouring.
Why learn with shapes?
Sudoku is often filed under "maths", but you never add anything — the puzzle is pure logic. Swapping the digits for shapes removes the "I'm bad at maths" wall and makes the deductions easier to see. If you're curious what that trains, read the benefits of visual sudoku.
Frequently asked questions
Do these strategies work for normal number sudoku too?
Yes — completely. Sudoku involves no arithmetic, so the digits 1–9 are just nine tokens. Every technique here works identically whether the symbols are numbers or the nine form9 shapes. Learning with shapes just keeps the logic front and centre.
Which technique should a beginner learn first?
Start with scanning and simple patterns, then hidden singles and naked singles. Those three solve nearly every easy puzzle on their own.
Do I ever need to guess in sudoku?
No. Every valid sudoku has exactly one solution reachable by pure logic. If you feel like guessing, there's a deduction you haven't spotted yet — back up and scan again rather than trial-and-error.