Sudoku Studio
Work through a 9×9 Sudoku with row, column and 3×3 box constraints. Generate clue tiers, check a pasted puzzle for exactly one solution, toggle pencil notes, request a naked or hidden single with its reasoning, and save or print your own board. Everything is calculated locally in your browser. Generated tiers describe clue targets, not a guaranteed human difficulty rating.
Key features
- Bounded randomized clue removal with a two-solution uniqueness check
- Custom 81-cell puzzle validation: malformed, contradictory, unsolvable and multiple-solution states
- Keyboard and touch entry, candidate pencil marks and highlighted conflicts
- Explainable naked-single and hidden-single hints with row, column or box context
- Explicit answer reveal, session JSON save/load and puzzle-only printable SVG
- Time/node budgets for solver and generation; local browser processing
How to use
- Choose a clue tier and generate, use the worked example, or paste a custom 81-cell puzzle.
- Select a cell and type 1–9, use the number controls, or toggle pencil-note mode to store candidates.
- Check conflicts and progress, then request a logical single-candidate hint when needed.
- Save the current board to JSON, load it later, or download a puzzle-only printable SVG.
- Reveal the full solution only after a separate confirmation.
Use cases
- Practice Sudoku without sending a puzzle to a server
- Check whether a classroom puzzle has a unique solution
- Print a clue-only board while keeping the answer hidden
Frequently asked questions
Are generated puzzles guaranteed to have one solution?
Yes. Each proposed clue removal is kept only when a bounded solver finds exactly one solution. If time or node limits prevent verification, the removal is rejected. Generation itself has a time limit and may ask you to retry.
Does the selected tier guarantee difficulty?
No. Gentle, standard and challenge are approximate clue-count targets, not a rating of the solving techniques a person needs. Random symmetry transformations and shuffled removal are not a uniform sample of all valid Sudoku grids.
What logic do hints use?
A naked single has one remaining candidate in its cell. A hidden single is the only cell in a row, column or box that can hold a digit. The tool reports the rule and location; it does not invent a guessing step.
Why can a custom grid be rejected?
A grid must contain exactly 81 digits, with 0 or . for blanks. Repeated digits in a row, column or box, no possible solution, multiple solutions or a solver time limit are shown separately. A saved session also must preserve its clues.
What is saved and printed?
JSON stores clues, your entries, pencil marks and tier, and stays in the file you download. The SVG and browser print view contain only the original clues; the answer is never included in the printable puzzle.
Privacy
Puzzle calculations run in the current tab. JSON and SVG files are created only on request; uploads are read locally and are not sent to a server.
Comments & questions