The classic number-placement puzzle
Sudoku
Six levels from Easy to Extreme, a Daily Challenge, notes, hints that explain the technique, and statistics. Free, no sign-in, plays in the browser.
How to play
- The goal. Fill the 9×9 grid so that every row, every column and every 3×3 box contains the digits 1 to 9 exactly once. The bold digits are givens; every puzzle here has exactly one solution.
- Entering digits. Tap or click a cell, then a digit on the pad (or type it). Its row, column and box light up, and every cell holding the same digit is highlighted. A digit that clashes with the solution turns red when Auto-check is on, and the mistakes counter moves.
- Notes. Switch Notes on (N) to pencil candidates into a cell as a small 3×3 grid. Placing a digit removes that candidate from the cells it can see when "Remove notes automatically" is on. Shift plus a digit writes a note without changing mode.
- Hints. Hint (H) fills one cell with the correct digit and explains the technique that finds it: a naked or hidden single, a pair or triple, a pointing pair, box-line reduction, an X-Wing, Swordfish or XY-Wing. Three per game, or unlimited in Settings.
- Mistakes. Three mistakes end the game. A Second chance keeps the board and moves the counter back to 2/3. Undo (U or Ctrl+Z) takes back any number of moves but never a mistake.
- Time. The timer runs from the first look at the puzzle and stops while paused (P); the board is hidden while paused. Your best and average times per level are kept in Statistics.
What is replicated
- Six levels — Easy, Medium, Hard, Expert, Master and Extreme — graded by the hardest technique a puzzle needs, 120 puzzles each, every one proved to have a single solution.
- Selected cell, highlighted row, column and box, all cells holding the same digit, duplicates in red, givens in bold.
- Number pad 1–9 with a remaining count under each digit; a digit fades once all nine are placed.
- Undo without limit, Erase, Notes with pencil marks in a 3×3 mini-grid, automatic note removal.
- Hint that fills a cell and explains the technique, three per game with an Unlimited hints setting.
- Mistakes 0/3, game over at three and a Second chance to play on; the limit can be switched off.
- Pause with the board hidden and a Resume button; the timer can be hidden.
- Statistics per level: games started, won, win rate, best time, average time, current and best streak.
- Win screen with time, level, mistakes and hints; New Game with a difficulty picker that asks before abandoning a game in progress.
- Settings: auto-check, highlight duplicates, highlight areas, highlight same digits, remove notes automatically, timer, sound, mistakes limit, unlimited hints.
- Daily Challenge: one puzzle per day from the date, with a calendar of completed days.
- Light and dark themes; the board fills a phone screen with the pad below and sits beside the pad on a desktop.
Additions of this page: puzzle numbers such as #hard-42 with shareable links (this page's own numbering), the game in progress surviving a reload, Shift+digit for a note, and earlier Daily Challenges playable from the calendar. Sounds are short synthesized clicks made in the browser.
Keyboard
| Arrows | Move the selection | 1–9 | Place a digit (a note in Notes mode) |
|---|---|---|---|
| Shift+1–9 | Toggle a note | Backspace, Delete, 0 | Erase the cell |
| N | Notes on / off | H | Hint |
| U or Ctrl+Z | Undo | P | Pause / resume |
| Esc | Deselect, close a dialog | Enter | Confirm a dialog |
The six levels
| Easy | Naked singles only — a cell with one candidate left. About 38 givens. |
|---|---|
| Medium | Hidden singles — a digit with one place left in a row, column or box. About 31 givens. |
| Hard | Naked and hidden pairs and triples, pointing pairs, box-line reduction. About 27 givens. |
| Expert | X-Wing, Swordfish or XY-Wing needed. About 25 givens. |
| Master | Beyond all of those techniques: chains or trial and error. About 24 givens. |
| Extreme | A Master puzzle with 22 or fewer givens (the proven minimum for any Sudoku is 17). |
Questions
What are the rules of Sudoku?
Fill the 9×9 grid so that every row, every column and every 3×3 box contains the digits 1 to 9 exactly once. A proper puzzle has a single solution, and every puzzle here has been checked for that.
How are the six difficulty levels decided?
By the hardest technique a human needs. Easy puzzles fall to naked singles alone, Medium needs hidden singles, Hard needs pairs, triples, pointing pairs or box-line reduction, Expert needs an X-Wing, Swordfish or XY-Wing, Master defeats all of those techniques, and Extreme is a Master puzzle with 22 or fewer givens.
How do hints work?
Press H or the Hint button and the game fills one cell with the correct digit and explains the technique that finds it, such as a hidden single in row 4 or a naked pair in box 7. A wrong entry on the board is corrected first. You get three hints per game unless you switch on Unlimited hints in Settings.
What happens after three mistakes?
The game is over, and you can take a Second chance: the board is kept and the counter goes back to two of three, so one more mistake ends the game again. A mistake is any digit that differs from the solution; Auto-check only controls whether it is shown in red. The Mistakes limit can be switched off in Settings.
What is the Daily Challenge?
One puzzle per day, the same for everyone, chosen from the UTC date. The level follows the weekday: Easy on Monday up to Extreme on Saturday, Hard on Sunday. Completed days are marked on the calendar.
Is my progress saved, and is anything sent anywhere?
Your settings, statistics, Daily Challenge calendar and the game in progress are stored in this browser only. The page makes no network calls of its own: there is no sign-in, no account and nothing to install.