Play eight verified Sudoku variants from Classic to Anti-knight, with six logic-rated levels, Daily history, training and layered rule-aware hints. Play Sudoku free in your browser — no download, no account.
Why play Sudoku here?
Classic, Diagonal, Thermo and Killer share one constraint-aware solver. Every grid is proved unique; pencil marks, keyboard play, unlimited undo and four-layer Hint all follow the selected rules.
How You WinFill the 9×9 grid so every row and column contains 1 through 9 exactly once, along with each 3×3 box or Jigsaw region, while satisfying every marking of the selected variant.
Grid
9 rows · 9 columns · nine 3×3 boxes
Symbols
Digits 1–9 · no arithmetic
Rules
8 verified variants · Classic through Anti-knight
Complete Rules
Each empty cell receives one digit from 1 through 9. The printed starting digits are givens and cannot be changed.
A digit cannot repeat within a row, a column or one of the nine bold 3×3 boxes.
Diagonal Sudoku also places 1–9 on each marked long diagonal; Thermo digits strictly increase from the round bulb to the tip.
In Killer Sudoku, digits inside a dashed cage add to its corner total and cannot repeat within that cage.
Kropki dots connect consecutive or 1:2 digits; Jigsaw replaces the regular boxes with nine outlined irregular regions.
An Arrow's shaft adds to its circled digit; Anti-knight prevents matching digits a chess knight's move apart.
The puzzle is complete only when all 81 cells are filled and every classic and selected-variant constraint holds everywhere.
Pencil marks are optional notes. They do not count as entries and do not affect whether the grid is valid.
A red entry conflicts with the unique solution or visibly breaks a row, column, box or selected-variant rule. Erase or undo it before relying on later deductions.
Your First Game
Scan one row, column or box at a time. Ask which digits are missing, then test where each missing digit could still go.
A naked single is a cell where eight digits have already been ruled out. The one remaining candidate must be the answer.
A hidden single belongs to a unit rather than a cell: several candidates may be written in a cell, but only that cell can hold one particular digit in the row, column or box.
Use Notes when two or three choices remain. Good notes record possibilities; they are not guesses.
If you are stuck, open Hint once for a direction. Open it again only when you need the technique or evidence.
Practical Strategy
Alternate between digit scanning and cell scanning. Looking only for nearly full rows misses digits whose only legal position is hidden in a roomy unit.
After placing a digit, revisit all three affected units. One answer often creates the next single immediately.
Keep pencil marks complete in the area you are analysing. Partial notes can make a false single look convincing.
When a digit's candidates inside one box all lie in the same row or column, that relationship can eliminate the digit elsewhere along that line — the foundation of locked candidates.
Winning and Special Rules
Daily mode maps the local calendar date to a fixed puzzle. Changing language does not change that day's grid.
Easy uses naked singles; Medium adds hidden singles; Hard adds locked candidates or pairs; Expert adds triples and X-Wing-class deductions. Labels come from a complete logical solve, not clue count.
The four Hint layers are nudge, technique, evidence and optional fill. Requesting a hint never fills the cell until you explicitly choose the last layer.
New game offers eight variants and six difficulty levels. Every variant can be started directly or explored through an optional interactive introduction.
Daily Sudoku belongs to Daily puzzles and is saved on this device. Today and yesterday are playable; completed dates can be revisited from the calendar.
Common Mistakes
Guessing between two candidates instead of looking for a constraint elsewhere. A guess can remain apparently consistent for a long time and poison later notes.
Treating the number of starting clues as difficulty. Their placement and the techniques required matter more than the count.
Writing only one of several possible pencil marks, then mistaking the incomplete note set for a logical single.
Looking at rows and columns but forgetting the box or the selected variant marking. Every answer must satisfy all applicable constraints simultaneously.
Sudoku FAQ
Do I need to be good at math to solve Sudoku?
No. The symbols happen to be digits, but you never add or multiply them. You only track which of nine symbols can still occupy each cell.
Does every Sudoku have only one solution?
A well-formed published puzzle should. Every puzzle in this player is checked by an exact solver and is released only when the solver finds exactly one solution.
What is a pencil mark?
It is a small candidate digit you keep in an empty cell. Pencil marks are your notes, not part of the final answer, and can be toggled without changing the puzzle rules.