Sudoku
Fill a 9×9 grid so that every row, column, and 3×3 box contains the digits 1–9 exactly once.
Sudoku is a classic and timeless logic puzzle that has captivated millions worldwide with its elegant simplicity and deep strategic challenge. Played on a 9×9 grid, the puzzle is divided into nine 3×3 subgrids (also called "boxes" or "regions"). At the start, some cells are pre-filled with numbers from 1 to 9. Your task is to fill in the remaining empty cells so that each row, each column, and each 3×3 box contains all the digits from 1 to 9 exactly once—no repeats, no omissions.
Played on a 9×9 grid divided into nine 3×3 boxes, the goal is simple yet deeply engaging: fill the grid so that every row, every column, and each 3×3 box contains all the digits from 1 to 9 exactly once. This means no number can repeat in any row, column, or box, creating a complex web of constraints that challenge your logical reasoning skills.
The puzzle begins with a set of pre-filled clues, and your task is to deduce the missing numbers using logic alone. Despite its numerical appearance, Sudoku is not a math game—it's a pure exercise in logic, pattern recognition, and deductive reasoning. Every puzzle has one unique solution, reachable through careful analysis without guessing.
This browser-based version of Classic Sudoku offers:
Solving a Classic Sudoku puzzle relies entirely on logic, patience, and pattern recognition—no arithmetic or guessing is needed. Here's a concise overview of the core solving techniques, from beginner to intermediate level:
1. Scan Rows, Columns, and Boxes
Start by looking at each row, column, and 3×3 box. Identify which numbers are missing, then check where a specific digit (e.g., "5") can legally go based on existing clues. If a number can only fit in one cell within a row, column, or box, place it there.
2. Use the "Single Candidate" Rule
In an empty cell, list all possible numbers (called pencil marks). If only one number fits without violating Sudoku rules, that's your answer.
3. Apply "Hidden Singles"
Sometimes a number appears as a candidate in multiple cells within a row/column/box—but it's the only place that number can go in that unit. Even if other candidates are present, that number must go there.
4. Eliminate Possibilities
As you fill in more numbers, each new digit eliminates options in its row, column, and box, often revealing new singles.
5. Work Systematically
Don't jump randomly—focus on one number at a time (e.g., "Where can 1 go in each box?") or one region (e.g., "What's missing in this row?"). This structured approach prevents oversight.
6. Avoid Guessing
Every proper Sudoku has a unique solution reachable through logic alone. If you feel stuck, revisit earlier steps—there's always a logical next move, even if it's subtle.
With practice, you'll recognize common patterns (like naked pairs, pointing pairs, or X-Wing in harder puzzles), but even the most difficult grids start with these fundamentals. Remember: slow and steady wins the Sudoku!
Fill in a number in every square so that each number appears exactly once in every row, every column, and every block outlined by thick lines.
To place a number, click a square to select it, then type the number on your keyboard. To remove a number, click a square to select it, then press the delete key.
Tip: On mobile devices, you can use a virtual keyboard to place numbers.