How to play
Sudoku is a logic puzzle played on a 9×9 grid that is split into nine 3×3 boxes. Some cells already contain digits. These are the clues, shown in bold black. Your job is to fill every empty cell so that each row, each column and each box contains the digits 1 to 9 exactly once. No arithmetic is involved; it is pure logic.
Press New game to choose a difficulty, select an empty cell and pick a digit from the number pad. The small number on each pad key shows how many copies of that digit are still missing, and a key fades out once all nine are on the board. Your game is saved automatically in this browser, so you can close the tab and carry on later.
Rules
- Every row, column and 3×3 box must contain each digit from 1 to 9 exactly once.
- The clues given at the start cannot be changed.
- Each puzzle has exactly one solution. Before a puzzle is shown, a solver checks that no second solution exists.
- A digit that does not match the solution counts as a mistake and turns red while Highlight mistakes is on. Two equal digits in the same row, column or box always get a red background.
- Hint fills one correct cell and is counted. Best times are saved per difficulty, but only for games finished without hints.
The difficulty levels are graded by the techniques a puzzle needs, not just by the number of clues:
- Easy: solvable with naked singles only. At every step some cell has just one possible digit.
- Medium: also needs hidden singles, where a digit fits in only one cell of a row, column or box.
- Hard: needs candidate techniques such as pointing pairs, box/line reduction, naked pairs or hidden pairs.
- Expert: as few clues as the generator can reach in a short time while keeping a single solution. Expect long searches and advanced techniques.
Controls
Mouse: click a cell, then click a digit on the pad. The buttons under the pad undo, erase, switch notes on or off and give a hint. The pause button hides the grid and stops the timer.
Touch: tap a cell, then tap a digit. On a phone the grid fills the screen width and the pad sits right below it.
Keyboard:
- 1–9: enter a digit, or toggle a note while notes are on
- Arrow keys: move around the grid
- Backspace or Delete: erase the selected cell
- N: switch notes on or off
- Ctrl+Z or U: undo (as many steps as you like)
- P: pause or resume
Entering the same digit again removes it. When you place a digit, it is also removed from the notes in the same row, column and box.
Tips and strategy
- Start with digits that already appear often. If six 7s are on the board, the last three are usually easy to place.
- Scan box by box. For each missing digit, rule out the rows and columns that already contain it and see where it can still go.
- Use notes once the obvious cells are done. Writing every candidate in a row or box makes pairs and pointing patterns visible.
- Select a filled cell to highlight every copy of that digit. It shows at a glance which rows and columns are still open for it.
- When you are stuck, look for a row, column or box with only two or three empty cells. Their missing digits often decide themselves.
- Avoid guessing. With exactly one solution there is always a logical next step, even when it is hard to find.
Frequently asked questions
Does every puzzle have exactly one solution?
Yes. After removing clues, the generator runs a solver that stops as soon as it finds a second solution. A puzzle is only shown when exactly one solution exists.
How is the difficulty decided?
A built-in grader solves each puzzle with the simplest techniques first and only moves on to harder ones when it has to. The level is set by the hardest technique it needed, so an Easy puzzle never requires more than naked singles.
What counts as a mistake?
Any digit you enter that differs from the solution. A mistake stays counted even if you undo it. You can switch off the red highlight and hunt for errors yourself; clashes between equal digits are always shown.
Is my progress saved?
Yes. The current grid, your notes, the timer and the undo history are stored in your browser on this device. Private browsing windows may forget them when they close.
Do I need an internet connection?
No. Puzzles are generated on your own device in well under a second, so the game keeps working offline once the page has loaded.
Why was my best time not saved?
Best times count only for puzzles solved without hints, so the record always reflects your own solving.
More free games
- Memory: match pairs of emoji cards in as few moves as possible.
- Klondike Solitaire: the classic patience card game.
- 2048: slide and merge numbered tiles to reach 2048.
- Minesweeper: clear the field without setting off a mine.
- Word Guess: find the hidden five-letter word in six tries.