Sudoku
Play Sudoku Online for Free
Fill the grid so every row, column and 3×3 box holds 1 to 9 once.
How to play
Pick Easy, Medium, Hard, Expert or Today’s puzzle on the start screen and press Play.
- Tap a square, then a number button.
- Tap the same number again to take it out, or press Erase.
- Turn on Pencil to jot down the numbers a square could still take. Placing a number removes it from the pencil marks in its row, column and box.
- A number that repeats in its row, column or box gets a wavy underline at once. A wrong number that repeats nothing isn’t marked until every square is filled. Then each wrong one is crossed out.
Hint clears a wrong number if you have one. Otherwise it places the next number and names the technique that finds it. Today’s puzzle has no Hint, though Undo works.
Controls
| Action | Touch | Mouse | Keyboard |
|---|---|---|---|
| Select a square | Tap it | Click it | Arrow keys or W, A, S, D; Home and End go to the row’s ends |
| Place a number | Tap a number button | Click a number button, or type 1 to 9 | 1 to 9; or Enter, arrows to a number button, Enter |
| Take a number out | Tap the same number, or Erase | Click the same number, or Erase | Backspace, Delete or 0 |
| Add or remove a pencil mark | Pencil on, then tap a number | Pencil on, then click a number | Shift with a number; N turns Pencil on or off |
| Undo | Undo | Undo | U, Z or Ctrl+Z |
| Hint (not in Today’s puzzle) | Hint | Hint | H |
| Pause or resume | Pause button | Pause button | Esc |
Tips and strategy
Ask where a number can go
An Easy puzzle often starts with 4 to 7 squares that can take only one number (a naked single). About 12 more are the only place left for some number in their row, column or box (a hidden single). Take one number at a time and check each box for it.
On Medium, use pencil marks once singles run out
On Medium, singles fill only about 15 squares. Then, 9 times in 10, the next step is pointing. Say the only squares in a box that can still hold a 4 are all in one row. The box’s 4 is in that row, so cross 4 off the rest of that row, outside the box.
On Hard, look for a Y-Wing
Nearly every Hard puzzle here uses one. Find a square with only 3 and 8 in pencil. If one square it sees (same row, column or box) has only 3 and 5, and another only 8 and 5, then one of those two is a 5 whatever the first holds. Cross 5 off every square that sees both.
About sudoku
The puzzle as it is played today is usually traced to 1979, when an American puzzle magazine printed it as Number Place, most likely made by Howard Garns. A Japanese publisher brought it to Japan in 1984 under a longer Japanese title, which it later shortened to sudoku, “number single”. From 1986 it set the given numbers in a symmetric pattern. Every puzzle here keeps that: turn the board half a turn and the givens sit in the same squares.
Frequently asked questions
- Does every sudoku here have only one solution?
- Yes. A puzzle is kept only when the game can finish it by logic and a full search finds exactly one solution, so you never have to guess.
- When does the daily sudoku change?
- At midnight UTC, and everyone gets the same puzzle that day. Its level follows the weekday: Easy on Monday and Tuesday, Medium on Wednesday, Thursday and Sunday, Hard on Friday, Expert on Saturday.
- What makes a hard sudoku hard?
- The techniques it needs. Easy needs only singles; Medium adds pointing, box/line reduction, and pairs, triples and quads. Hard needs an X-Wing or a Y-Wing, and Expert at least one of simple coloring, Swordfish, XYZ-Wing or Jellyfish.
- Can I stop a puzzle and finish it later?
- Yes, in the same browser on the same device. Each level and the daily keep their own unfinished puzzle, saved after every move with its time. An unfinished daily is gone once the day changes.
