Sudoku Unlimited
Four grid sizes. Four difficulty levels. Endless uniquely solvable puzzles.
How to play Sudoku
Choose a 4×4 Mini, 6×6 Compact, 8×8 Wide or 9×9 Classic grid. Fill every empty cell with a digit from 1 through the selected size. Each digit must appear exactly once in every row, column and outlined box. The starting clues cannot be changed, and every puzzle has one answer that follows from the visible clues.
Sudoku strategy
Scan for a single missing digit
Start with rows, columns or boxes that are nearly complete. List the missing digits and check which empty cells are blocked by matching numbers in their crossing row or column.
Use candidate notes
When a cell has several possibilities, turn Notes on and record them. A cell with one remaining candidate is solved. A candidate that can appear in only one cell of a row, column or box is also forced, even when that cell still shows other notes.
Compare boxes with their rows and columns
If every possible place for a digit inside one box lies on the same row, that digit cannot appear elsewhere on that row. The same box-line interaction works vertically and opens many Hard and Expert grids.
Difficulty levels
Easy grids begin with more digits and expose frequent single placements. Medium removes more direct clues, Hard requires longer candidate chains, and Expert starts sparsest. Every bundled grid is symmetrical, uses an original clue arrangement and is verified to have exactly one solution.
Share a fixed-seed challenge
The challenge panel below every board creates a link containing the exact grid size, difficulty and puzzle seed. Send it to a friend and they will start from the same clues, making solve times, mistakes and hint counts directly comparable.
Frequently asked questions
What are the rules of Sudoku?
Fill every row, column and outlined box with each digit for the selected grid size exactly once. A 4×4 puzzle uses 1 through 4, while the largest classic grid uses 1 through 9.
Which Sudoku sizes can I play?
Choose 4×4 Mini with 2×2 boxes, 6×6 Compact with 2×3 boxes, 8×8 Wide with 2×4 boxes, or 9×9 Classic with 3×3 boxes. Every size has Easy, Medium, Hard and Expert puzzles.
Does every puzzle have one solution?
Yes. Every included puzzle is checked offline by a solver and published only when its starting clues lead to exactly one completed grid.
How do notes work?
Turn Notes on, select an empty cell and enter any candidate digits you want to remember. Placing a correct full-size digit automatically removes that candidate from its row, column and box.
Can I play entirely with a keyboard?
Yes. Arrow keys move the selection, the available number keys enter a digit, Backspace erases, N toggles notes, H uses a hint, P pauses and Control-Z or Command-Z undoes.
Is my unfinished Sudoku saved?
Yes. Entries, notes, mistakes, hints and elapsed time are saved automatically in this browser.
Can a friend play the same Sudoku?
Yes. Every unlimited puzzle has a fixed seed. Copy or share its challenge link and the recipient receives the same size, difficulty, clues and solution.