Sudoku Generator

How the Zeloku Sudoku generator works

Every generated Sudoku on Zeloku is produced by a three-stage pipeline. First, a full 9×9 solution grid is constructed with seeded backtracking, producing a complete grid that satisfies every row, column and box constraint. Cells are then removed one at a time. After each removal, a solver checks whether the board still has exactly one solution. If uniqueness is lost, that clue is restored.

Finally, the board receives an estimated complexity score. The current Easy, Medium, Hard and Expert bands use different clue targets plus this estimate. These labels are practical starting points, not a guarantee that a particular named technique will appear.

Difficulty calibration

Zeloku offers four broad difficulty bands. Solving time varies by experience, and two boards with the same clue count can feel very different. The technique library explains useful patterns, but the labels below do not promise a fixed technique set.

• Easy — more starting clues and a shorter expected solve. See easy Sudoku.
• Medium — a balanced daily challenge. See medium Sudoku.
• Hard — fewer clues and more candidate tracking. See hard Sudoku.
• Expert — the lowest clue target and widest search space. See expert Sudoku.

Looking for a batch?

Our printable packs bundle 16–20 generated puzzles per PDF, ready for travel, classrooms or coffee breaks. Each pack includes a full answer key on the final pages.

What about custom Sudoku for developers?

If you're building something and want programmatic puzzles, our Sudoku solver accepts an 81-character string and checks the board and returns its solution or a basic next-step hint. A public generator API is on the roadmap — reach out via the about page if you have a use case that would benefit from early access.

Generator FAQ