Sudoku: Rules and How to Play
A Sudoku race: everyone gets the same puzzle, starts on 3-2-1 and races to finish first while watching each other's progress. 1–20 players, about 6 minutes. Free in your browser, no sign-up.
Objective
Sudoku is a puzzle where you fill a 9×9 grid with the numbers 1–9 so that no row, column or bold 3×3 box contains the same number twice. Here everyone gets the same puzzle, and the faster you finish, the higher you rank.
Setup
- 1–20 players. Alone, you can chase your best time or race the CPU.
- Choose Intro (6×6), Easy, Medium, Hard or Expert. Intro uses 1–6 on a 6×6 grid with 3×2 boxes.
- Everyone gets the same puzzle and starts together on 3-2-1 (the numbers are hidden until then).
How to play
- Tap an empty square to select it, then tap a number below. Tap the same number again to clear it.
- Turn on [Notes] to pencil in small candidate numbers. [Erase] empties the selected square and [Undo] takes back your last change.
- If the same number appears twice in a row, column or box, it is marked (! and an underline) and a short reason appears where you tapped. There is no penalty for mistakes.
- There are no turns: everyone solves their own grid at their own pace. You can't see other grids; the top three names and their progress (%) are shown at the edge of the screen, plus your own rank if you are 4th or lower.
- Progress is the share of the originally empty squares that you have filled without a clash.
Winning and scoring
- The puzzle is solved when every square is filled with no clashes. Finishers are ranked by time.
- You can keep playing after the target time. Finishers within the limit rank ahead of later finishers, ordered by completion time. Players who press [Quit] rank last. Rounds that go past the limit earn no points.
- The round ends when all human players finish or quit, even if CPUs are still solving. Humans can keep playing if a CPU finishes first. After 60 minutes from the start, results use the progress so far. Unfinished players rank by progress. [Play again] starts the next round.
- With the handicap on, the winner's next puzzle is one level harder (more if they keep winning). Ranking is still by time.
Defaults on this site
| Item | Default on this site |
|---|---|
| Players | 1–20 players (set automatically by the party size) |
| Turn time limit | None by default (the host can set 30 or 60 seconds) |
| If someone drops mid-game | Reopening on the same device returns you to your seat. If you do not return, the CPU plays in your place. |
| Draws | In ranked play, a draw counts as halfway between a win and a loss for your rating. |
| Source of the rules | Based on the standard reference rules |
Rules supervised by Qdan, Inc. (based on the standard reference rules)
House rules
Defaults follow the standard reference rules. The party can change these.
| Name | Description | Default | Changeable |
|---|---|---|---|
| Difficulty | How hard the puzzle is. Intro is 6×6; the others are 9×9. | Easy | Yes |
| Handicap the winnerHandicap the winnerWhen on, the previous round's winner solves a puzzle one level harder. Each further win adds another level; losing returns you to the chosen difficulty. Even when puzzles differ, ranking is by finishing time. | Only the winner gets a puzzle one level harder next time. | Off | Yes |
| Time limit | Your target time. Play continues after it and the clock counts overtime. At 60 minutes from the start, results use your progress. | 10 min | Yes |
| Auto-clear notesAuto-clear notesCleared notes come back together with the number when you press [Undo]. | Placing a number clears it from the notes in the same row, column and box. | On | Yes |
Terms
- Box
- A block of squares inside bold lines: 3×3 on a 9×9 grid, 3 wide × 2 tall on the 6×6 Intro grid.
- Notes
- Small candidate numbers you pencil into a square.
- Progress
- The share (%) of originally empty squares you have filled without a clash.
- Handicap
- A setting that makes the winner's next puzzle one level harder.
- Personal best
- Your fastest finish at that level on this device.
FAQ
What are the rules?
Fill the empty squares with 1–9 so that no row, column or bold box repeats a number. The puzzle is solved when the grid is full.
What happens if I make a mistake?
Clashing numbers are marked. There is no penalty; fix it and carry on.
How is the ranking decided?
By finishing order (shortest time first). Players who timed out are ranked by progress, and players who quit rank last.
Play now with these rules
Last updated 2026-10-05 · Run by Qdan, Inc.