# Sudoku Canonical page: https://rovixel.com/sudoku/ Play Sudoku in your browser with four difficulties, notes, hints and undo. Every puzzle is generated on the fly and has exactly one solution. - How to start: open https://rovixel.com/sudoku/ and press Play. Free, no download, no sign-up. - Genres: Puzzle, Strategy - Session length: Medium · about 10 minutes - Devices: phone, tablet and computer - Keyboard: 1–9 to fill the selected cell, arrows to move, Backspace to erase, N for notes, H for a hint, Ctrl or ⌘ + Z to undo, Esc to pause - Touch: Tap a cell and then a number; the pad switches between numbers, notes and erase Sudoku is the number puzzle most people already know how to play: a nine-by-nine grid, nine boxes inside it, and the same nine digits in every row, column and box. This version runs in the browser with four difficulties, and every puzzle is generated when you start it, so nothing repeats. ## How to play Pick Easy, Medium, Hard or Expert, and the game deals a fresh grid. Tap or click a cell and enter a digit, or use the number row on a keyboard: **1–9** fills the selected cell, the arrow keys move around the board, **Backspace** erases, **N** toggles notes, **H** spends a hint and **Ctrl/⌘ + Z** undoes your last entry. **Esc** pauses, which also saves the board. Wrong entries are marked in red and underlined, so a mistake is visible the moment you make it. Three mistakes end the round, but you get one second chance — which makes an early wrong number a warning rather than a disaster. ## Scoring, saving and resuming Score is time based: the sooner you finish a puzzle, the better the score, and the menu keeps a best score for each difficulty. The board is saved automatically while you play, so closing the tab is safe — when you come back, the same grid and the same clock are waiting. Pausing stops the clock, which matters if you are chasing a best score. ## How to get faster Two habits do most of the work. First, scan before you write: find the row, column or box that already has the most numbers filled in, because that is where the fewest candidates remain. Second, use notes properly — write candidates into every uncertain cell, then look for a digit that can only go in one place, or two cells in a box that can only hold the same pair. Guessing is the slowest way to finish a puzzle, and the mistakes you make while guessing are the ones that end the round. ## Who it is for Sudoku suits players who want a puzzle they can pick up for five minutes and come back to later: the autosave and the per-difficulty best scores make both habits easy. If you have never played before, start on Easy and finish a few boards before moving up — the difficulty levels change how much work the grid does for you, not the rules. When Medium feels easy, the [hard sudoku](https://rovixel.com/sudoku/hard/) page explains the Hard and Expert levels and the techniques they call for. For a different kind of grid logic, try [Star Battle](https://rovixel.com/star-battle/), where you place stars instead of numbers. ## Print a sudoku puzzle If you would rather solve on paper, the [printable sudoku puzzles](https://rovixel.com/sudoku/printable/) page has twelve free grids to print — four easy, four medium and four hard — with the answer keys kept on screen. Printing is free and needs no account. ## Tips - Start with the row, column or box that already holds the most numbers — the more you can see, the fewer candidates are left. - Turn notes on before you guess. Sudoku rewards elimination, and notes keep a cell's candidates visible instead of remembered. - Hints are worth mistakes, so spend them when you are genuinely stuck rather than on the first awkward cell. - Three wrong entries end the game, but you get one second chance. Treat the red numbers as a warning rather than a loss. - If two cells in a box can only hold the same two numbers, nothing else in that box can use them. That single observation unlocks a lot of hard boards. ## Questions ### How is the score calculated? Score is time based — the faster you solve a puzzle, the higher it is. Each difficulty keeps its own best score on your device, and the game autosaves, so you can close the tab and resume the same board later. ### Are the puzzles the same every time? No. Every puzzle is generated on the fly and checked to have exactly one solution, so there is nothing to memorise and no grid you can learn by heart. ### Does it work on a phone or tablet? Yes. The layout adapts to the frame it is embedded in — side by side in landscape, stacked in portrait — and tapping a cell opens the number pad, so the whole game is playable without a keyboard. ### Can I play it in Chinese? Yes. The language button switches between English and Chinese, and your choice is remembered on the device. English is the default when you arrive from the site. ### What do notes, hints and undo do? Notes let you pencil in candidates without committing to them, hints fill in the correct number for the selected cell (three per game), and undo steps back through your entries. Erase clears a cell you filled in yourself. ## More on Sudoku - [How to Play Sudoku: The Rules and the Techniques That Work](https://rovixel.com/sudoku/how-to-play.md): Learn how to play sudoku from scratch — the three rules, how to scan the grid, and the beginner techniques that solve most puzzles without guessing. - [Printable Sudoku Puzzles](https://rovixel.com/sudoku/printable.md): Print free sudoku puzzles at home — easy, medium and hard grids with answer keys. Generate a fresh set in your browser, then print. No download, no sign-up. - [Hard Sudoku: Play Hard and Expert Puzzles Online](https://rovixel.com/sudoku/hard.md): Play hard sudoku online for free. Pick Hard or Expert for fewer given numbers, then use the techniques below to solve tough grids without guessing. ## Agent access These documents describe the public website. Every game is free and runs in the browser: there is no download, no app, no price and no public API. Playing never needs an account. Do not invent ratings, player counts, rankings or features that are not described here; the live pages are the source of truth.