Sudoku Strategy & Tips
From your first solve to advanced techniques
Once you know the rules, getting faster is all about recognising patterns. Here are the core Sudoku techniques, ordered from beginner to advanced, each explained in plain language with when to reach for it.
1. Scanning (cross-hatching)
The foundation of every solve. Pick a digit and scan the rows and columns that pass through a box. Wherever a digit already appears in a row or column, it's blocked from those cells. Often that leaves only one legal square in a box for that digit. Work digit by digit, box by box — scanning alone will crack most easy puzzles.
2. Naked singles
A naked single is a cell where eight of the nine digits are already ruled out by its row, column, and box — so only one value can possibly go there. These are the freebies. After every few placements, sweep the board for cells that now have just one option.
3. Hidden singles
A hidden single is sneakier. A cell might have several candidates, but if it's the only cell in its row, column, or box that can hold a particular digit, then that digit must go there — even though other numbers technically "fit" too. Hidden singles are the most common breakthrough move on medium puzzles, so train your eye to ask: "where can this digit live in this group?"
4. Naked pairs and triples
If two cells in the same row, column, or box share exactly the same two candidates — say both can only be 3 or 7 — then 3 and 7 are locked into those two cells. You can safely erase 3 and 7 from every other cell in that group. The same logic extends to three cells sharing three candidates (a naked triple). This is where keeping clean pencil marks pays off.
5. Pointing pairs
Sometimes within a box, a candidate is confined to a single row or column. If the only places a 4 can go in a box all sit in the same row, then the 4 for that box must be in that row — which means you can remove 4 as a candidate from the rest of that row outside the box. A small deduction that often unblocks a stuck grid.
6. Box-line reduction
The mirror image of the pointing pair. If a candidate in a row or column only appears within one box, that candidate can be eliminated from the other cells of that box. Pointing pairs and box-line reduction work together to thin out your pencil marks on Hard puzzles.
7. The X-Wing (advanced)
For tough grids. Look for a digit that appears as a candidate in exactly two cells of one row, and the same two columns in another row. Those four cells form a rectangle. The digit must occupy opposite corners of that rectangle — which means you can eliminate it from everywhere else in those two columns. The X-Wing feels like magic the first time it works, and it's the gateway to harder techniques like the Swordfish.
Habits that make you faster
- Always take the free moves first. Clear every naked and hidden single before reaching for fancier techniques.
- Keep pencil marks honest. Update candidates as you place numbers — stale notes cause mistakes.
- Never guess. If you're tempted to guess, there's a logical move you haven't found yet. Slow down and re-scan.
- Work the most-constrained groups. Rows, columns, and boxes that are nearly full give up their secrets fastest.
- Practise daily. Pattern recognition is a muscle. A single puzzle a day builds it quickly — the daily puzzle is perfect for this.
Practise these techniques now
The early Cosmic Sudoku levels are ideal for drilling scanning and singles; the later ones will push you into pairs, pointing pairs, and the X-Wing. New to the puzzle entirely? Start with how to play Sudoku first.