How to Play Sudoku

What Is Sudoku?

Sudoku is a logic puzzle played on a 9×9 grid divided into nine 3×3 boxes. Some cells are pre-filled with numbers (called "givens"), and your job is to fill in the rest. Despite using numbers, sudoku requires no math — it's purely about logic and deduction.

The puzzle was popularized in Japan in the 1980s, and its name roughly translates to "single number." Today it's one of the most widely played puzzles in the world, loved for its elegant simplicity and satisfying depth.

The Rules

Sudoku has just three simple rules:

1. Each row must contain the numbers 1 through 9, with no repeats.
2. Each column must contain the numbers 1 through 9, with no repeats.
3. Each 3×3 box must contain the numbers 1 through 9, with no repeats.

Every properly constructed sudoku puzzle has exactly one valid solution. You should never need to guess — every cell can be determined through logical reasoning.

Getting Started

When you first look at a sudoku grid, it can feel overwhelming. Here's a practical approach for beginners:

1. Look for rows, columns, or boxes with few empty cells. If a row already has 7 of 9 numbers filled in, you only need to figure out which two numbers are missing and where they go.
2. Scan for numbers that appear frequently. If the number 5 already appears in 7 of the 9 boxes, the remaining two 5s are highly constrained and often easy to place.
3. Work through one number at a time. Pick a number (say, 1) and try to place it in every box where it's missing. This systematic approach catches placements you might otherwise miss.

Basic Solving Techniques

These techniques will get you through most easy and many medium puzzles:

• Naked single — When a cell has only one possible number (all other numbers already appear in its row, column, or box), that number must go there. This is the most fundamental technique.
• Hidden single — When a number can only go in one cell within a row, column, or box, it must go there — even if that cell could theoretically hold other numbers too.
• Scanning — For a given number, scan each row and column to eliminate possibilities in a box. If a box is missing the number 7, and rows and columns eliminate all but one cell in that box, that's where the 7 goes.

Common Mistakes to Avoid

• Guessing too early. If you find yourself guessing between two numbers, step back and look for cells where you can be certain. There's always a logical next step.
• Forgetting the 3×3 boxes. New players often focus on rows and columns but overlook the box constraint. Always check all three constraints before placing a number.
• Tunnel vision. If you're stuck on one area of the grid, move to a different section. Solving cells elsewhere often unlocks the area you were stuck on.
• Not double-checking. Before moving on, verify that your placement doesn't create a duplicate in any row, column, or box. Catching errors early saves a lot of backtracking.

Playing on Good Fun Puzzles

Our online sudoku player makes solving easy and distraction-free:

• Keyboard entry — Click a cell and press 1–9 to enter a number. Press 0, Backspace, or Delete to clear it. Use arrow keys to navigate the grid, or Tab to jump to the next empty cell.
• Visual highlighting — When you select a cell, its row, column, and 3×3 box are highlighted, making it easy to see which numbers are already used. Cells with the same number as your selection are also highlighted.
• Error checking — Toggle "Show Errors" to highlight conflicting numbers in real time. Duplicates in a row, column, or box are shown in red.
• Reveal tools — Stuck on a cell? Use "Reveal Cell" to uncover one cell, or "Reveal Puzzle" to see the full solution.
• Auto-save — Your progress saves automatically. Close the tab, come back later, and everything will be exactly as you left it.
• Timer — Track your solving time and try to beat your personal record.
• Mobile friendly — On phones and tablets, a built-in number pad appears so you can solve without a keyboard.