What is Sudoku Generator/Solver?

A free Sudoku generator and solver. Generate new puzzles at any difficulty — easy, medium, hard, or expert — or paste in your own puzzle and let the solver find the solution using backtracking. Great for practice or checking your answers.

The generator builds a complete grid with backtracking, then removes cells until you reach your chosen difficulty (easy, normal, difficult, or expert). The solver finds the unique solution in milliseconds, and the check button flags conflicts in red. The hint button names the next logical step — a naked or hidden single — then fills that cell, so you learn the technique instead of just getting the answer. You can also auto-fill every cell's pencil candidates, and a running mistake counter and end-of-solve stats track how cleanly you finished.

How to use

1. Choose a difficulty level and tap Generate to create a new Sudoku puzzle.
2. Fill in cells by clicking and typing numbers 1-9, or paste an existing puzzle.
3. Tap Solve to instantly find the solution, or tap Check to validate your answers.

When to use

• Cross-checking a newspaper or magazine Sudoku you can't finish.
• Generating a fresh puzzle at the right difficulty for your morning coffee.
• Teaching kids the rules of Sudoku with hints rather than full solutions.

Result

You're stuck on a newspaper Sudoku. Enter the given numbers into the grid, tap Solve, and the tool fills in all 81 cells in under a second using a backtracking algorithm.

FAQ

How does the solver actually work?

It uses recursive backtracking: try a number, check if it breaks row, column, or 3x3 box rules, move on. If a branch dead-ends, it rolls back and tries the next candidate. For valid puzzles it finds the answer in under a second.

Does every Sudoku puzzle have exactly one solution?

Standard Sudoku puzzles do — that's part of the definition. If a grid has two or more valid solutions it's not really a Sudoku, just a partial fill. Our generator only outputs grids with one unique solution.

What's the difference between difficulty levels?

Easy leaves around 40 clues and only needs basic scanning. Normal gives ~34, requires pencil marks. Difficult drops to ~28 and forces deduction chains. Expert sits at ~22-24 and may need advanced techniques like X-Wing or Swordfish.

Can I paste a puzzle from somewhere else?

Yes. The fastest way is the Paste puzzle button — drop in the 81-digit string (0 for blanks) that most Sudoku sites use, and it loads straight into the grid. You can also click any empty cell and type, using the arrow keys to move around. Hit Validate to confirm the clues have one unique solution, then Solve or Check.

Is the hint button cheating?

It depends on your goal. For learning, hints teach you which deduction unlocks the next move. For competition, you'd avoid them. Use one hint when fully stuck, then study how that cell resolves before continuing on your own.

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