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  1. Home
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  3. Sudoku
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Sudoku

Sudoku puzzle generator and solver with auto-generated valid puzzles, hint system, and error highlighting

Place the numbers 1 through 9 so that every row, column, and 3×3 box contains each digit exactly once. Sudoku is pure logic, no math required, no guessing needed. From gentle warm-up puzzles to fiendishly difficult grids, there is always a challenge waiting.

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Sudoku: a worked example

A cell’s row already contains 1-5 and 7-9, and its column and box rule out nothing further.

Cell candidates

Row has {1,2,3,4,5,7,8,9} → only 6 is missing
Sudoku produces

Result

The cell is forced to 6 (naked single)

A "naked single" is the simplest deduction: when a cell has exactly one remaining candidate it must take that value, with no guessing. Chaining singles, hidden singles, and locked candidates solves most puzzles purely by logic, the solver verifies a unique solution exists.

Fill the Grid, Train Your Brain

Place the numbers 1 through 9 so that every row, column, and 3×3 box contains each digit exactly once. Sudoku is pure logic, no math required, no guessing needed. From gentle warm-up puzzles to fiendishly difficult grids, there is always a challenge waiting.

How to use

  1. 1Select a difficulty level to generate a new puzzle.
  2. 2Click an empty cell and enter a number from 1 to 9.
  3. 3Use notes mode to pencil in candidate numbers for tricky cells.
  4. 4Complete the entire grid with no conflicts to solve the puzzle.
  5. 5Use hints if you get stuck, they highlight the next logical step.

Key features

  • Multiple difficulty levels from easy to expert
  • Pencil marks / notes mode for candidates
  • Error highlighting to catch mistakes early
  • Hint system that teaches solving techniques
  • Timer with pause functionality
  • Undo/redo support
  • Auto-save progress on each puzzle

Common use cases

  • Daily mental exercise

    A daily Sudoku puzzle keeps logical thinking skills sharp and provides a satisfying routine.

  • Focus and mindfulness

    The deep concentration required makes Sudoku an effective way to practice sustained focus.

  • Travel companion

    Works offline after loading, perfect for flights or commutes.

  • Learning logical reasoning

    Sudoku teaches deduction and elimination in an accessible, non-intimidating format.

How it works

Solving Sudoku relies on scanning for forced placements, using elimination within rows, columns, and boxes, and applying techniques like naked pairs and hidden singles as puzzles get harder. The satisfaction of completing a tough grid through pure reasoning is unmatched. Multiple difficulty levels ensure both beginners and experts find puzzles that stretch their skills.

Frequently asked questions

Do I need to be good at math?

Not at all. Sudoku is about placement logic, not arithmetic. You could use letters or symbols instead of numbers.

Is guessing ever required?

No. Every well-constructed Sudoku puzzle is solvable through logic alone.

What if I make a mistake?

Error highlighting will flag conflicting numbers so you can correct them. You can also undo moves.

How long does a puzzle take?

Easy puzzles can be done in 5-10 minutes. Expert-level grids might take 30 minutes or more.

Private by design

The game runs entirely in your browser. No account is needed and no gameplay data is collected.