Sudoku
Play free sudoku online with five difficulty levels. Every puzzle has a unique solution, with notes, hints, undo and a timer - generated right in your browser.
What are the rules of sudoku?
Fill the 9x9 grid so that every row, every column and each of the nine 3x3 boxes contains the digits 1 to 9 exactly once. No digit may repeat within a row, column or box.
Does every puzzle have a unique solution?
Yes. Each puzzle is generated in your browser and verified with an exact solver, so it always has exactly one valid solution - just like a properly constructed newspaper sudoku.
What do the difficulty levels mean?
The five levels mainly differ in how many cells are given at the start. Beginner leaves the most clues, while Expert removes more cells, requiring advanced techniques and deeper logic chains.
How do pencil notes work?
Turn on the Notes button and the numbers you enter become small pencil marks inside the cell instead of a final answer. Use them to track candidates, then switch back to normal mode to commit a digit.
What does the conflict highlighting show?
When you select a cell, all identical numbers in the same row, column and 3x3 box are highlighted, so you can instantly see which values are blocked. Direct rule violations are shown in red.
How many hints do I get?
Three hints per game. Each hint fills one empty or incorrect cell with the correct value, which is a good way out of a dead end without revealing the whole solution.
Is the game playable on a phone?
Yes. The board scales to the screen and a numeric keypad sits below it for touch input. On desktop you can use the keyboard: arrows to move, 1-9 to enter digits, Backspace to erase.
Is sudoku generated on a server or in my browser?
In your browser. The generator and the uniqueness checker run locally in a web worker, so the game works offline after the page loads and nothing about your play is transmitted anywhere.
How to Use Sudoku
This sudoku game generates every puzzle right inside your browser, and each one is verified to have exactly one solution. Everything - generation, checking, hints - happens locally on your device.
- Pick a difficulty from the dropdown (Beginner to Expert) and press New game, or just start playing the puzzle that loads automatically.
- Tap a cell to select it, then use the number pad below the grid or your keyboard's 1-9 keys to fill it in. Tap the same number again to clear it.
- Turn on Notes to write small pencil candidates in a cell - perfect for tricky sections. Press Erase or Backspace to clear a cell.
- Select any cell to highlight all matching numbers in its row, column and box, and press Check at any time to see which filled cells are wrong.
- Stuck? Use one of your three Hints to reveal a correct digit, Pause to hide the board, or Solve to reveal the full solution.
- When the grid is complete and correct, the timer stops and your finishing time is displayed.
On desktop, arrow keys move between cells and Tab starts a fresh game - much faster than the mouse once you get going.
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