Sudoku

What this tool does

Sudoku generates a fresh, uniquely-solvable 9x9 puzzle at your chosen difficulty, with live conflict highlighting for any digit that breaks the row/column/box rule, and automatic detection when the puzzle is fully and correctly solved.

Sudoku is the classic number-placement puzzle: fill a 9x9 grid so every row, column, and 3x3 box contains the digits 1 through 9 exactly once, with a logical, unique solution reachable from the given starting clues.

This generator builds a fresh, uniquely-solvable puzzle every time by filling a complete valid grid and then removing cells down to your chosen difficulty, with live conflict highlighting and automatic win detection.

How to use Sudoku

1. Choose easy, medium, or hard difficulty.
2. Click any empty cell and type a digit 1–9.
3. Cells highlighted red conflict with another digit in the same row, column, or 3×3 box.
4. Fill every cell correctly to see the "Solved!" status.

Tips for better results

• Harder difficulty means fewer starting clues are given, requiring more logical deduction and fewer direct "only one possibility" cells to start from.
• Pre-filled given cells (shown bolder) can’t be edited, only cells you need to fill yourself can be changed.
• A red-highlighted cell means that specific digit conflicts with another cell in the same row, column, or 3x3 box, not necessarily that it’s wrong relative to the puzzle’s unique solution, just that it currently breaks a Sudoku rule.
• Click "New puzzle" at any time for a completely fresh grid at the same difficulty, every generated puzzle has exactly one valid solution.

Common use cases

• Playing a quick logic puzzle during a break without needing a newspaper or app download.
• Practicing Sudoku strategy at a specific difficulty level repeatedly.
• A screen-free-feeling mental exercise that still works entirely in the browser.
• Generating an unlimited supply of fresh, unique puzzles rather than a fixed daily puzzle.

Common mistakes to avoid

• Confusing a conflict highlight with "this puzzle is unsolvable," every generated puzzle always has exactly one valid, reachable solution, a red highlight just flags an immediate rule violation in your current entries, not a dead end.
• Trying to edit a pre-filled given cell, those are locked by design, only the empty cells you need to solve can be changed.
• Guessing randomly rather than using logical deduction, classic Sudoku solving relies on elimination (checking which digits are already impossible for a cell based on its row/column/box) rather than trial and error.