How to play & controls Free Sudoku Online
GameNow Sudoku decides how hard a puzzle is by solving it the way a person would. A built-in solver knows twelve named techniques, from Naked Single to Swordfish, and always tries the easiest one first. A puzzle's level comes from the hardest technique it needs plus the total amount of work, and every clue removed while the puzzle is built is checked against that solver, so no puzzle ever requires guessing.
Every puzzle grows from a single seed number. Today's puzzle takes its seed from the UTC date and the level, so everyone who opens Hard on the same day gets the same grid, and both duel players build their boards from one shared seed. Your progress is saved as that seed plus the moves you made, and the daily ranking replays those moves on the server before it accepts a time.
Hints explain instead of just filling a cell: they name the technique, light up the cells that prove it, and can tidy your notes in one step. After the puzzle you can revisit those exact positions as short quizzes.
Modes
Today's puzzle
Signed-in players get four puzzles a day, one per level, identical for everyone; a new set starts at 00:00 UTC. A hint-free solve you submit goes onto that level's ranking once the server has replayed it, and rankings are kept for 30 days.
Practice puzzle
Choosing a level while signed out, or pressing Play again after any solo puzzle, deals a fresh puzzle at that level with the same tools. Its time only updates the personal best stored on your device.
Duel
Two signed-in players who chose the same level get the same puzzle, with no Undo or Hint, only Resign. If the 12 minutes run out, more correctly filled cells wins, then fewer mistakes; otherwise it is a draw.
Controls
| Action | Mouse & keyboard | Touch | Gamepad |
|---|---|---|---|
| Select a cell | Click, or arrow keys | Tap the cell | D-pad, or pointer + A |
| Place or clear a digit | 1–9 (same digit again clears it); Backspace, Delete or 0 erases | Number pad; Erase | Pointer on the pad or Erase + A |
| Write or remove a note | Shift+1–9, or N for Notes mode | Notes, then digits | Pointer on Notes + A |
| Undo (solo only) | Z | Undo | Pointer on Undo + A |
| Hint (solo only) | H; Esc closes it | Hint, then Place it / Update notes / Close | Pointer on Hint + A; B closes |
| Resign (duel) | Resign, then confirm | Resign | Pointer on Resign + A |
| Solo result screen | Enter = Play again, Esc = Menu | Tap a button | Start = Play again, B = Menu |
Strategy tips
Let the number pad count for you
With an empty cell selected, the pad greys out every digit already in its row, column or box, and the line above the board lists what is left. One lit button means a Naked Single; a greyed-out digit you are sure of means a wrong digit sits in that row, column or box.
Know what each level can demand
A puzzle graded Easy needs only singles, Normal adds Pointing Pair and Claiming, Hard can require pairs, triples and quads, and only Expert can require X-Wing, XY-Wing or Swordfish. Practice puzzles show that grade in the header. A stalled Hard puzzle calls for subsets, not wings.
Write notes freely, fix with Undo
A correct digit removes itself from the notes in its row, column and box. A wrong digit leaves neighbouring notes alone but wipes the notes in its own cell; Undo brings them back, Erase does not.
Know when a hint is spent
A hint is used the moment the panel opens, since the panel already states the answer. If wrong digits are on the board, Hint only asks you to remove them first; that is free and does not keep a daily time off the ranking.
Solve a ranked attempt in one sitting
The server notes when you first open each level of Today's puzzle, and your ranked time cannot be shorter than the time since then minus 10 seconds. Switching tabs stops the on-screen clock, not the server's.
In duels, fill clean and finish units
Completing a row, column or box for the first time locks three of your opponent's empty cells for 4 seconds. Every fifth correct first fill in a row hides two of their filled cells for 6 seconds, and every fifteenth plants four false notes. A mistake resets the streak, and only one effect goes out per move.
Spotting planted notes
A planted note is always a digit already in that cell's row, column or box, never one you wrote. Shift plus that digit removes it on a keyboard; on touch that digit is greyed out, so Erase the cell's notes instead.
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