How to Play Sudoku

Sudoku is a logic puzzle played on a 9×9 grid. You never need to guess and you never need math — just careful reasoning. This guide covers the rules, how to make your first moves, and the techniques that take you from beginner to expert. When you're ready, play a puzzle or build your own.

The rules

The grid is divided into nine rows, nine columns, and nine 3×3 boxes. Some cells start filled with "givens". Your job is to fill every empty cell with a digit from 1 to 9 so that:

• Each row contains the digits 1–9 with no repeats.
• Each column contains the digits 1–9 with no repeats.
• Each 3×3 box contains the digits 1–9 with no repeats.

A proper Sudoku has exactly one solution that can be reached by logic alone. Every puzzle generated here is checked for that single unique solution before you ever see it.

Making your first moves

The fastest way to start is scanning. Pick a digit — say 5 — and look at the rows, columns, and boxes where a 5 already appears. Those lines "eliminate" cells. When a 3×3 box has only one cell left where a 5 can legally go, you've found a placement. Repeat this for each digit and you'll clear the easy cells quickly.

Core solving techniques

Naked singles

If a cell can only hold one possible digit — because the other eight already appear in its row, column, or box — that digit must go there. These are the bread-and-butter moves of easier puzzles.

Hidden singles

Sometimes a cell has several candidates, but a digit can only fit in one cell within a row, column, or box. Even though the cell isn't "naked", that digit is forced there.

Pencil marks

Harder puzzles are easier with pencil marks — small notes of the candidate digits for each cell. As you place numbers, candidates get eliminated and patterns emerge. In the player you can add notes by hand, or turn on auto-candidatesto fill every cell's legal digits automatically, with notes cleaned up as you solve.

Pairs and pointing

When two cells in a unit share the same two candidates (a "naked pair"), those two digits can be removed from every other cell in that unit. When all candidates for a digit in a box line up in a single row or column, you can eliminate that digit from the rest of that row or column. These eliminations crack expert boards.

Difficulty levels

Difficulty mostly comes down to how many givens you start with and which techniques are required. On Sudoku Builder you can jump straight into any level:

• Easy — plenty of givens; solvable with scanning and naked singles.
• Medium — fewer givens; expect to lean on hidden singles.
• Hard — sparse givens; pencil marks and pairs become essential.
• Expert — minimal givens; advanced eliminations required.

Tips for improving

• Work one digit or one box at a time instead of jumping around the grid.
• Never guess — if you're stuck, there is always a logical next step to find.
• Use pencil marks early on harder puzzles so eliminations are visible.
• If you get stuck, a hint can reveal the next logical placement to keep you moving.

That's everything you need. Start a puzzle, and once you're comfortable, try building one to share with a friend.