How to Play

Sudoku has three simple rules. Master these, and you understand the entire game.

The Three Rules

Rule 1: Every Row

Each horizontal row must contain the digits 1 through 9 exactly once. No repeats, no missing numbers.

Rule 2: Every Column

Each vertical column must contain the digits 1 through 9 exactly once.

Rule 3: Every Box

The grid is divided into nine 3×3 boxes. Each box must contain the digits 1 through 9 exactly once.

The Goal

Fill in every empty cell so that all three rules are satisfied simultaneously. There's only one correct solution for each puzzle.

Given Numbers

Every puzzle starts with some cells already filled in—these are called givens or clues. You cannot change these numbers. They're displayed in a darker color to distinguish them from your entries.

The number of givens determines the puzzle's difficulty:

  • Easy: ~35+ givens
  • Medium: ~30 givens
  • Hard: ~25 givens
  • Expert: ~22 givens
  • Evil: ~17-20 givens

Making Progress

The key insight is that the three rules work together. When you can't find a number using just one rule, combine them:

  1. Look at a row—which numbers are missing?
  2. For each empty cell in that row, check its column and box
  3. If only one number fits all constraints, that's your answer

What Makes a Valid Puzzle?

A proper Sudoku puzzle has exactly one solution. If you reach a point where you must guess, either:

  • You missed something—look again
  • The puzzle is poorly constructed (rare in quality sources)

Never guess randomly. Sudoku is solvable through pure logic.