WonderSift / operating notes
WonderSift Sudoku
Daily puzzle + unlimited practice
Play one shared daily Sudoku or continue with unlimited practice, with logical hints that explain the next step before revealing it.
- Classic 9 by 9
- Four audited levels
- Explain-first hints
- No account required
Choose a mode and difficulty, then play
Preparing a verified Sudoku...
Three rules, then play
How to play
- Fill every empty cell with 1 through 9.
- Each row, column, and outlined 3-by-3 box uses every digit once.
- Use Notes for possibilities, not guesses.
Sudoku is logic, not arithmetic: the digits are symbols, and nothing needs to be added.
The classic contract
Rules of the grid
Read the complete rules and logic note
WonderSift Sudoku is a classic 9x9 logic puzzle built for a satisfying daily solve, quiet practice, and explanations that teach rather than simply expose an answer.
- Fill every empty cell with a digit from 1 through 9.
- Each row contains every digit exactly once.
- Each column contains every digit exactly once.
- Each outlined 3x3 box contains every digit exactly once.
Calculation vs. logic
The digits do not add, multiply, or measure anything. They are nine distinct symbols, and every move follows from where a symbol can or cannot appear.
Learn before you leap
Beginner lesson
Learn the first solving move
The interactive desk includes a small four-by-four demonstration. It teaches exactly-once logic without pretending the teaching grid is a public game mode.
- Start by scanning one row, column, or box for a digit that has only one possible home.
- Pencil marks record possibilities, not guesses. Remove a candidate only when a row, column, box, or demonstrated pattern rules it out.
- WonderSift's lesson uses a small teaching grid before returning you to the full 9x9 board.
A disclosed difficulty ladder
Technique ladder
See what each difficulty expects
Easy: naked singles and hidden singles.
Medium: locked candidates, naked pairs, and hidden pairs.
Hard: triples, X-Wing, and XY-Wing.
Expert: quads, Swordfish, simple coloring, and bounded alternating-inference chains.
Method shown
How difficulty is assigned
Open the generator and verification method
Each base puzzle is produced by an original deterministic generator and checked by an independent exact solver for one and only one completion. The full solution is not shipped in the public puzzle record.
A separate human-style solver records reproducible logical steps. Its hardest required technique assigns the public difficulty, and the same step evidence powers explain-first hints without treating clue count as a shortcut for difficulty.
- The exact solver and human-style solver are separate so explanatory logic cannot establish uniqueness by itself.
- A puzzle belongs to the lowest complete technique tier that solves it; unsupported grids are rejected rather than mislabeled Expert.
- Daily puzzles are fixed by US Eastern calendar date, while practice selections avoid recently played base IDs when possible.
How uniqueness is verified
A separate exact solver counts completions and accepts a puzzle only when that count is exactly one. The explainable solver then grades the accepted grid independently, so a logical trace never doubles as the uniqueness proof.
Rule reference
Play your way
Keyboard and accessibility
See keyboard controls and printing
- Use the arrow keys to move between cells and digits 1 through 9 to enter a value.
- Backspace or Delete erases an entry; the note shortcut switches pencil marks on or off.
- Undo and redo are available by keyboard, and Escape closes temporary panels without trapping focus.
Printing a puzzle
Use the Print control in the game desk. The print view removes navigation, settings, hints, results, and every advertising position so the grid remains the only working surface.
Useful answers
Questions worth asking
Is WonderSift Sudoku free to play?
Yes. Daily and Practice play launch without an account or payment, and the core puzzle does not require a newsletter subscription.
Is Sudoku calculation or logic?
It is a logic puzzle. Digits are symbols here: the rules depend on placement and exclusion, not arithmetic relationships between the numbers.
Will a refresh erase my puzzle?
An ordinary refresh should resume the locally saved puzzle. Clearing this site's storage can remove it, so export a backup if completed history matters to you.
How are hints different from answers?
The first hint identifies and explains the next supported logical step. A direct reveal is separate and marks that solve as assisted.