sudoku

About This Game

Sudoku delivers the quintessential number logic puzzle in a clean, feature-rich digital format perfect for both newcomers and seasoned solvers. Fill a 9x9 grid so that every row, column, and 3x3 box contains the digits one through nine exactly once. With multiple difficulty settings from gentle introductory puzzles to fiendishly challenging expert grids, the game scales seamlessly to your skill level. Helpful features like pencil marks for candidate tracking, error highlighting, and an optional hint system make the solving experience smooth without diminishing the intellectual satisfaction of cracking each puzzle through pure logic. This free browser game is the ideal daily brain exercise.

How to Play sudoku

The 9x9 grid is divided into nine 3x3 boxes. Some cells are pre-filled with numbers — these are your clues. Your task is to fill every empty cell with a digit from one to nine such that no digit repeats within any row, column, or 3x3 box. Start by scanning each row, column, and box to identify cells where only one digit is possible — these are called naked singles and are the easiest deductions. Next, look for hidden singles: cells where a particular digit can only go in one spot within a row, column, or box, even if that cell has other candidates. Use the pencil mark feature to jot down possible candidates in each empty cell. As you fill in confirmed digits, revisit neighboring cells to eliminate candidates and uncover new singles. For intermediate puzzles, learn pointing pairs and box-line reduction techniques. A pointing pair occurs when a candidate within a box is restricted to a single row or column, allowing you to eliminate that candidate from other cells in the same row or column outside the box. Advanced puzzles may require naked pairs, triples, or X-wing patterns. A naked pair is two cells in the same unit sharing exactly two candidates — other cells in that unit cannot contain those two digits. Never guess randomly. Every cell in a well-constructed Sudoku can be solved through logical deduction alone. If you feel stuck, step back and rescan the entire grid for constraints you may have missed. The hint system can nudge you by highlighting a cell that has a logical next step, helping you learn new techniques without spoiling the solution entirely.

Not sure which number fits? Follow our Sudoku pencil marks and hidden singles guide to narrow down candidates before guessing.

Highlights

• Multiple difficulty levels from beginner to expert
• Pencil mark system for tracking digit candidates
• Error highlighting to catch mistakes immediately
• Optional hint system that teaches solving techniques
• No download required — play free in any browser
• Unlimited puzzle generation for endless practice

Tips & Tricks for sudoku

• Scan for naked singles first — cells where only one digit is possible
• Use pencil marks to track candidates and eliminate them systematically
• Look for hidden singles where a digit fits in only one cell within a row, column, or box
• Never guess — every Sudoku puzzle has a purely logical solution path
• When stuck, rescan the entire grid for overlooked constraints before using hints