Sudoku online
A fresh puzzle at your level — notes, hints and undo included.
Click a square or use the arrow keys, then type 1–9. N turns notes on and off, Shift + digit adds a note, Backspace erases, Ctrl+Z undoes.
Nothing leaves your device
This tool runs entirely in your browser. What you type, play or record here stays on your device: nothing is uploaded or saved on a server.
Example
Stuck on a Hard puzzle: what Check, Hint and Undo each do — and what they count
Level “Hard”, then New game: 27 squares are given, 54 are left to fill, and there is exactly one solution. Half-way through nothing seems to fit. These are the tools on the pad, and what each adds to the tally shown when you solve it.
| Button or key | What it does | What it counts |
|---|---|---|
| Notes (N) | Small candidate digits in a square; placing a digit takes it out of the notes in the same row, column and box | Nothing |
| A digit that repeats one in its row, column or box | Highlighted at once while “Show conflicts as you type” is on | 1 mistake, once per square and digit |
| Check | Marks every square that differs from the solution, or says “Everything so far is correct” | Each wrong digit not yet counted, as a mistake |
| Hint | Fills the selected square if it is empty or wrong, otherwise the square with the fewest possible digits; that square is then fixed | 1 hint |
| Undo / Redo (Ctrl+Z) | Steps back through up to 300 moves | Nothing |
| Pause | Hides the board and stops the clock; switching to another tab pauses too | Nothing |
When the last square is right, “Solved!” shows your time with the hints and mistakes beside it, and “New best” if you beat this level’s best time in this browser. Easy puzzles give 40 squares, Medium 32, Expert usually 24 (now and then up to 27).
How it works
- Choose a level and press New game.
- Fill every row, column and 3 × 3 box with 1 to 9: tap a square, then a number; use Notes for pencil marks.
- Use Check or a Hint when you are stuck; your time and best time are shown when you solve it.
Frequently asked 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. The given numbers can’t be changed.
- Does every puzzle have one solution?
- Yes — each puzzle is checked to have exactly one solution, so it can always be solved by logic, without guessing.
- What are notes?
- Pencil marks: small candidates you write in a square while you work it out. When you place a number, it is removed from the notes in the same row, column and box.
- Will I lose my game if I close the page?
- No — the game in progress is saved in this browser and comes back when you return, one per level.
- How many numbers are given at each level?
- Of the 81 squares: Easy 40, Medium 32, Hard 27, Expert usually 24 (sometimes up to 27). Fewer givens mean longer chains of reasoning, but every puzzle still has exactly one solution.
- Do hints and mistakes affect my best time?
- The time counts whatever help you used. Hints and mistakes are shown next to it when you solve the puzzle, so you can tell a clean solve from a helped one.
- Is anything sent anywhere?
- No. The puzzles are made and played in your browser.