One to nine, once each in every row, every column and every 3×3 box. No install, no account, and your unfinished grid is waiting when you come back.

Getting started

1. On the title screen pick a level — Easy, Normal, Hard or Expert — and press START. Your choice is remembered, and if a saved grid exists it is reopened instead of a new one.
2. Tap a cell to select it; its row, column and box are highlighted. Tapping a filled cell also highlights every copy of that digit on the board.
3. Enter digits with the number pad or the 1–9 keys. Under each pad button is a count of how many of that digit are still missing; a digit that has been placed nine times is dimmed. Pressing the same digit again erases it.
4. Use Notes, Erase, Undo and Hint from the tool row as needed. The same row has New puzzle and Today's sudoku; if a game is in progress you are asked before it is abandoned.
5. When all 81 cells are filled with no conflicts the win card appears with your time and mistake count. If it was today's puzzle you can enter a nickname and submit your time.

How sudoku works

You fill a 9×9 grid with digits. There is exactly one rule: every row, every column and every 3×3 box must contain 1 to 9 without repeating. The numbers printed at the start are fixed; the rest you work out by logic. Every puzzle here has a single solution and is solvable to the end by pure reasoning — you will never have to guess.

Four difficulty levels

Difficulty here is set by the techniques a puzzle demands, not by how many cells are blank. That keeps each level feeling consistent.

• Easy — plenty of clues; cells fall one after another.
• Normal — more blanks, but no advanced moves needed — just a thorough scan.
• Hard — you'll want notes, weighing candidates against each other.
• Expert — patterns that span several lines at once (X-Wing and friends).

In more detail: Easy and Normal are both solvable with singles alone — "only one digit fits this cell" or "this digit has only one place left in this row, column or box" — and differ only in how many clues are left: at least 40 for Easy, at least 30 for Normal. Hard requires candidate-elimination moves such as naked pairs and triples, pointing pairs (a digit confined to one line inside a box) and box/line reduction (a digit confined to one box along a line), with around 28 clues. Expert puzzles need hidden pairs, X-Wing or XY-Wing. Every grid is checked to be solvable to the end with just these techniques before it is served, which is also what guarantees a unique solution.

Using notes

Jot uncertain candidates as notes. Turn notes on, press a digit to pencil it in, press it again to rub it out. When you commit a real number, matching notes in the same row, column and box are tidied up for you. Undo is unlimited, so experiment freely.

Put the same digit twice in a row, column or box and the square turns red. Nothing stops you from placing it, though, and the game never checks your entries against the solution — whether a digit is right is for your own logic to decide.

Screen layout and keyboard controls

Above the grid you see Time, Left, Mistakes, Level and Puzzle number; on today's puzzle the number is replaced by a calendar mark. Mistakes go up by one each time you place a digit that breaks a rule — a digit already present in the same row, column or box — never simply for differing from the solution. On a computer everything works from the keyboard: 1–9 to enter, Backspace, Delete or 0 to erase, Space or N to toggle notes, and the arrow keys to move the selection. The grid resizes to the space available, so it fits a phone held upright as well as a desktop window.

When you get stuck

Hint points at a cell that can be pinned down right now and names the logic that does it — it never fills the number in for you, and there is no "reveal the solution" button, because the whole pleasure of sudoku is the moment you see it yourself. When nothing jumps out, pick a single digit and hunt for it across the entire grid; that scan cracks most stalls.

You get five hints per puzzle, and the Hint button shows how many remain. If nothing can be pinned down from what is on the board, the game says so; if the board is in a contradictory state because one of your digits is wrong, it tells you that instead — a few presses of Undo is usually the fastest fix.

Resuming and records

A puzzle in progress is saved to this browser every second. Close the tab, come back, press START and you continue with the same time, mistakes, notes and hints used. Only one puzzle is kept: finishing it or starting a new one clears the save. The win card shows your time and mistakes, and on today's puzzle also whether you set a personal best, plus a nickname field (up to 12 characters) for the leaderboard. The share button builds a result card link carrying your time, mistakes, puzzle number and level so a friend can try to beat it.

The daily puzzle and puzzle numbers

Every layout has a number. Today's sudoku comes from the date (Korea Standard Time), so everyone in the world gets the same grid — ideal for racing a friend on equal terms — and only today's puzzle (Normal) goes on the leaderboard, a top 10 sorted by fastest time. The puzzle number is shown above the grid and on the shared result card, so you can confirm you and a friend solved the same one.

More quiet puzzle games

If you like thinking games you can play alone, try Klondike Solitaire, FreeCell where virtually every deal is solvable, or Pyramid Solitaire for short rounds. All free, all in the browser, identical on phone and desktop.

Frequently asked questions

Can I see the solution?

No. Hints that point out a solvable cell and its reasoning are as far as the help goes. Every puzzle is built to be solved by logic alone, so when you are stuck, take a hint, find the cell, and follow the reasoning it names.

I have used all five hints — can I get more?

Not on the current puzzle. A new puzzle starts with five again, but the count does not refill mid-game.

My saved puzzle disappeared

Either you finished it, started a new puzzle or today's puzzle, or the browser's site data was cleared. Only one game is saved at a time and it does not sync across devices.

When does today's puzzle change?

At midnight Korea Standard Time. Wherever you are, the switch happens at the same moment for everyone.

Related tools

• Minesweeper — another classic built on numeric clues and deduction, with its own daily board and leaderboard
• Block Puzzle — fill a 10×10 grid at your own pace, no timer
• 2048 — the sliding number puzzle with a score leaderboard