Sudoku
Play free Sudoku puzzles in your browser. Every puzzle is newly generated and has exactly one solution, in Easy, Medium or Hard. Pencil marks (notes), conflict highlighting, keyboard input and a timer with your best time for each difficulty. Your game is saved automatically.
What is Sudoku?
Sudoku is a number puzzle on a 9×9 grid divided into nine 3×3 boxes. Some cells are already filled in. Fill in the rest so that every row, every column and every 3×3 box contains each digit from 1 to 9 exactly once. You never need to guess: a proper Sudoku has only one solution, and it can be found by logic.
How to play
- Click or tap a cell to select it. The row, column and box of the cell are highlighted, as well as every cell with the same digit.
- Type a digit 1–9, or press a button on the number pad. Press Backspace, Delete or 0 (or the erase button) to clear the cell.
- Turn on Notes (or press N) to write small pencil marks instead. Entering a digit removes the same pencil mark from its row, column and box.
- Move the selection with the arrow keys.
- Digits that clash with another digit in the same row, column or box turn red.
- The puzzle is solved when the grid is full and correct. Your time is saved as a best time for that difficulty.
Difficulty
| Difficulty | Given digits |
|---|---|
| Easy | 40 |
| Medium | 32 |
| Hard | about 24–26 |
Every puzzle is generated in your browser and checked to have exactly one solution.
Strategy
Use the techniques in this order. Start with the simple ones and only move to the next one when you are stuck.
1. Scanning (cross-hatching)
Pick a digit, for example 5. For each 3×3 box that does not have a 5 yet, cross out the rows and columns that already contain a 5. If only one empty cell of the box is left, the 5 goes there. Go through the digits 1 to 9 this way. Easy puzzles can be solved with scanning alone. Selecting a cell highlights every cell with the same digit, which makes scanning easier.
2. Naked single
Look at one cell and rule out every digit already in its row, column and box. If only one digit is left, write it.
3. Hidden single
Look at one row, column or box. If a digit can go in only one of its cells, it goes there, even if that cell has other candidates.
4. Pencil marks
On Medium and Hard puzzles, turn on Notes (N) and write every possible digit in each empty cell. When you place a digit, it is removed automatically from the notes in the same row, column and box, and new singles often appear.
5. Naked pairs and triples
If two cells in the same row, column or box have exactly the same two candidates (for example both 3 7), those two digits must go in those two cells. Remove 3 and 7 from the notes of every other cell in that unit. The same works for three cells that share three candidates.
6. Pointing pairs and box/line reduction
- Pointing: if, inside a box, a digit can only go in cells that are on one row (or column), it must go on that row inside this box. Remove it from the rest of that row outside the box.
- Box/line reduction: the other way round. If, in a row, a digit can only go in cells inside one box, remove it from the other cells of that box.
7. X-Wing (for hard puzzles)
If a digit can go in exactly two cells in each of two rows, and those cells are in the same two columns, the digit must be in two opposite corners of that rectangle. Remove it from every other cell in those two columns. (It also works with columns and rows swapped.)
General advice
- Do not guess. Every puzzle here has exactly one solution, so there is always a logical next step.
- When you are stuck, check your notes again: one missed candidate can hide the next move.
- A red digit clashes with another digit in its row, column or box. Fix it right away, because everything you place after it may be wrong too.
FAQ
What does the Hint button do?
It finds the next digit you can place by logic, using the same techniques as the Strategy section (singles, pointing, box/line reduction, pairs, triples and X-Wing), and explains each step. The cell blinks, and Fill in writes the digit for you. If one of your digits is wrong, the hint points that out first. Hints are worked out from the digits on the board, not from your notes.
If none of these techniques can make progress (this happens on some Hard puzzles), the hint shows the answer of the cell with the fewest candidates instead.
A puzzle solved with hints is not counted for your best time.
Is my game saved?
Yes. The puzzle, your digits and notes, the timer and your best times are saved in this browser.
Does it tell me when a digit is wrong?
It only shows clashes with digits already on the board, as on paper. A digit that does not clash can still be wrong, which you will find out later.
Where can I see my past games?
Open Records & history below the game. It shows your best result for each difficulty and your last 10 games with the date and time and the number of hints used. They are saved in this browser only.