Does each puzzle have only one solution?

Yes. After removing clues the generator runs a solver on the remaining grid and only keeps a removal if the puzzle still has exactly one unique solution, so there is never any guessing ambiguity.

What do the difficulty levels mean?

Difficulty controls the number of given clues — easy keeps around 40, medium around 32, and hard around 26. Fewer clues generally means a harder solve.

How is a fully-solved grid created first?

The generator fills an empty 9x9 grid with a randomised backtracking algorithm that respects the row, column, and 3x3 box rules, producing a valid complete solution before any clues are removed.

How does it remove clues without breaking uniqueness?

It tentatively clears cells and re-checks that only one solution remains. If removing a cell would create a second solution, that cell is kept, which guarantees a single answer.

Can I print the puzzle or save it as a PDF?

Yes. Use your browser's print or save-as-PDF function on the generated grid. The solution stays hidden until you click Show solution, so you can print the puzzle alone.

Is my puzzle generated on a server?

No. The full backtracking solver and puzzle generation run in your browser, so nothing is sent anywhere.

Sudoku Generator — Gera Tools

Generate fresh 9x9 sudoku puzzles in easy, medium, or hard difficulty, each verified to have a single unique solution. It is ideal for printable puzzle sheets, classroom packs, or a quick brain-teaser.

How it works

The generator runs three stages entirely in your browser:

Build a full grid. A randomised backtracking algorithm fills an empty board so every row, column, and 3x3 box contains 1–9 once — a complete, valid solution.
Remove clues. Cells are cleared one at a time according to the chosen difficulty’s clue target (about 40 easy, 32 medium, 26 hard).
Guarantee uniqueness. After each removal a solver checks the board still has exactly one solution. If clearing a cell would allow a second solution, that cell is restored.

This means every puzzle is solvable by logic alone, with no guessing.

Example

Difficulty	Approx. given clues	Typical solve effort
Easy	~40	Straightforward scanning
Medium	~32	Some candidate elimination
Hard	~26	Advanced techniques

Generate, print or save as a PDF, then reveal the answers with one click when you are ready. Everything happens in your browser — nothing is uploaded.