Sudoku Solver
Fill in your own puzzle from scratch, or generate one and watch the algorithm solve it step by step.
or generate a puzzle to get started
How Our Sudoku Solver Works
Our solver uses a highly optimized backtracking algorithm that explores every possible placement and backtracks instantly when it hits a dead end. Most puzzles — even the hardest graded puzzles — are solved in milliseconds.
Choose Solve Animated to watch the algorithm think in real time. Drag the speed slider to slow it down and observe how backtracking exploration works.
Frequently Asked Questions
How do I use the Sudoku solver?
Click any empty cell, then tap a number on the number pad (or use your keyboard). Leave unknowns empty, then click Solve Instant.
Does it solve all Sudoku puzzles?
Yes — any valid 9×9 Sudoku with at least one solution. Puzzles from newspapers, apps, or books all work.
What if my puzzle has no solution?
The solver will alert you. This usually means a clue digit was entered in the wrong cell.
Is it free?
100% free, no sign-up required, no usage limits.
How to Play Classic Sudoku
1 Rules
- ✓ Fill every row with the digits 1–9, no repeats.
- ✓ Fill every column with the digits 1–9, no repeats.
- ✓ Fill every 3×3 box with the digits 1–9, no repeats.
- ✓ Pre-filled clue cells cannot be changed.
2 Strategies
- 💡 Scanning: Sweep each row, column, and box to identify which digits 1–9 are missing — the missing set is the only valid input for that unit.
- 💡 Elimination: For any empty cell, cross out all digits already present in its row, column, and 3×3 box. One digit remaining means you have the answer.
- 💡 Hidden Singles: If a digit fits in only one cell within a row, column, or box — place it there immediately, regardless of how many other candidates the cell has.
Tip: Stuck? Use Solve Instant to reveal the full solution, or Solve Animated to watch the backtracking algorithm explore every possibility in real time.