Sudoku looks intimidating because of the grid, but the rules fit on a beer mat. You'll be solving easy puzzles by the end of this page.
1. Understand the grid
Nine rows, nine columns, and nine 3×3 boxes. Each of those twenty-seven groups must contain the digits 1 through 9 exactly once. Most cells start blank; a few are filled in for you as clues. The whole puzzle is a logic problem about where the remaining digits go.
That's it. There's no "operator" between digits, no math, no hidden words. If a row already has a 5, no other cell in that row can be a 5.
2. Scan one digit at a time
The fastest opening move is to pick a digit — say 5 — and search every box for a place to put it.
- If a 5 is already in a row, every other cell in that row is ruled out for 5.
- Same for columns.
- If a box already has a 5, no other cell in that box can be a 5.
When you find a box where only one cell still has room for the 5, place it. Repeat for every digit. You'll often place ten or fifteen digits before you have to slow down.
3. Look for naked singles
A naked single is a cell where eight of the nine digits are already in its row, column or box. There's only one digit left that can fit. Place it.
After every placement, re-scan the row, column and box of the digit you just placed. Naked singles often cascade — one triggers two, which triggers a third. More on naked singles.
4. When to start using pencil marks
When scanning stops finding moves, switch on pencil marks. Write the candidate digits — every digit that could possibly go in the cell — in small text inside each empty cell.
It's slower than scanning, but it unlocks every technique beyond singles: pairs, triples, X-wings, the lot. Don't reach for pencil marks too early; you'll spend twenty minutes writing them when a sixty-second scan would have placed the same digits. Pencil-mark workflow.
5. Never guess
Every Sudokly puzzle has exactly one solution, reachable with pure logic. If you're tempted to guess, you've missed something — back up, scan again, and look harder. Guessing works on bad puzzles. The good ones reward patience.
What to do when you're stuck
- Scan a different digit. The one giving you trouble might need another digit placed first.
- Check the cells with the fewest pencil marks. A cell with two candidates is one logical step from being placed.
- Look at the box with the most given numbers. It's usually the easiest to crack.
- Take a break. Five minutes away from the grid solves more puzzles than five more minutes of staring.
Ready
Pick a level and start. Easy puzzles will give you the feeling of the game. Medium will introduce pencil marks. By hard you'll be reaching for named techniques.