Fill the 9×9 grid so every row, every column, and every 3×3 box contains each digit 1–9 exactly once. Tap a cell to select it, then tap a digit on the keypad — or use a number key. NOTES mode lets you pencil in candidates without committing.
Start with rows, columns, or boxes that already have many digits — they constrain the rest. Look for "naked singles" (cells with only one possible value) and "hidden singles" (boxes where a digit can only legally go in one place). Pencil-mark candidates and eliminate them as you commit digits.
Sudoku is a logic-based number-placement puzzle. Fill a 9×9 grid with digits 1 through 9 so that every row, every column, and every 3×3 box contains each digit exactly once. The puzzle starts with some cells already filled (clues); a properly-formed sudoku has exactly one solution and is deducible by logic alone — no guessing required.
Tap a cell, then tap a digit 1–9 to place it. Use pencil marks to record what's still possible in each cell — essential at hard and expert difficulty. As you place a digit, eliminate it from the same row, column, and 3×3 box. The puzzle is complete when every row, column, and box contains 1–9 with no duplicates.
| Technique | Description | Difficulty |
|---|---|---|
| Naked single | Cell has only one possible digit after eliminations | Easy |
| Hidden single | A digit has only one possible cell in a row, column, or box | Easy |
| Naked pair / triple | Two (or three) cells in a unit share the same two (or three) candidates | Medium |
| Pointing pair / triple | A box's only spots for a digit lie in one row or column — eliminate from the rest of that row/column | Medium |
| X-Wing | Two parallel rows have two candidate cells each in the same two columns — eliminate that digit elsewhere in those columns | Hard |
| Swordfish | X-Wing extended to 3 rows / 3 columns | Expert |
| Coloring / chains | Trace a candidate's implications through the grid until it forces a contradiction | Expert |
Every well-formed sudoku has exactly one solution and is logically deducible. The minimum number of clues for a unique-solution sudoku is 17 (proven by computer search, 2012). Most published expert puzzles solve with X-Wing + swordfish + unique-rectangle techniques; harder ones require chains.
Fill the 9×9 grid with digits 1–9 so each row, each column, and each 3×3 box contains every digit exactly once. Some cells start pre-filled.
Naked single: a cell has only one possible digit. Hidden single: a digit has only one possible cell in a row, column, or box. Both are the easiest deductions.
Small notes inside an empty cell listing the digits still possible there. As you fill cells and eliminate possibilities, erase marks accordingly. Most expert puzzles are unsolvable without them.
Every well-formed (single-solution) sudoku is logically solvable in principle. In practice, expert puzzles may require techniques most humans don't use day-to-day.
Difficulty sets the number of starting clues: 40 on Easy, 32 on Medium, 28 on Hard and 24 on Expert. Every puzzle has exactly one solution. Fewer clues usually means harder deductions, though the technique needed varies from puzzle to puzzle.
Each puzzle is built in your browser. The generator fills a complete, valid grid at random, then visits the cells in random order and tries removing each clue. After every removal it counts solutions, stopping as soon as it finds a second one. If the grid no longer has exactly one solution, the clue goes back. Because of this check, every puzzle here has a single unique solution.
Difficulty only sets how many clues the generator aims to leave: about 40 on Easy, 32 on Medium, 28 on Hard and 24 on Expert. Puzzles are not graded by the techniques they need, so two puzzles at the same level can feel quite different. If no more clues can be removed without breaking uniqueness, a puzzle can end with a few more clues than its target.
Daily uses the same generator with a fixed number sequence seeded from the current UTC date, aiming for 34 clues. Everyone gets the same grid on the same UTC day. Each daily is numbered from January 1, 2025. Solving it records your daily solve count and streak of consecutive days in your browser, and offers a Share button with the daily number, your time and your mistake count, but not the grid. Links ending in #daily open straight into that day's puzzle.
Selecting a cell shades its row, column and box and highlights every cell with the same digit. On a keyboard, 1 to 9 enter a digit (the same digit again clears it), Backspace, Delete or 0 erase, N toggles notes, and arrow keys move the selection, wrapping at the edges. Only the daily streak and solve count are stored; a puzzle in progress is lost on reload.
Sudoku on Board Gaming Hub is a full 9×9 grid with four difficulty presets — Easy, Medium, Hard, and Expert — plus pencil marks and undo. No account, no timer pressure unless you bring your own. This guide covers the techniques that take you from first fill to confident Expert grids.
Each row, column, and 3×3 box must contain digits 1–9 exactly once. Every technique is just a consequence of that constraint plus the givens already on the board.
Toggle pencil mode and note every possible digit per cell. Update marks after each placement — stale marks cause errors on Hard and Expert boards. On Easy and Medium, many puzzles solve with singles only if marks stay current.
If two cells in a unit share the same two candidates and only those two, eliminate those digits from other cells in the unit (naked pair). The same logic extends to triples. This is the bridge technique between Medium and Hard.
An X-Wing appears when a digit’s candidates in two rows align in the same two columns (or vice versa), letting you remove that digit from other cells in those columns. Expert puzzles on the hub may require X-Wing, swordfish, or simple coloring — if stuck, step back and re-check for hidden singles after a fresh mark pass.
Levels differ only in how many clues you start with (40, 32, 28 or 24), so treat these as typical experiences rather than rules.