Mistakes

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Easy. Tap a cell, then a digit. Hold a digit for a note.Easy. Click a cell, then a digit. Hold a digit for a note.

Logic puzzle

Fill every row, column, and box with the numbers 1 to 9.

Sudoku is a logic puzzle played on a 9x9 grid. Some cells start with a digit; you fill in the rest so that every row, every column and every 3x3 box holds the digits 1 to 9 exactly once. Every puzzle here has one solution and can be solved by reasoning alone, without guessing.

Updated 4 October 2026

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Why you will love it

Never a guess

Every puzzle has one solution and is checked to be solvable by logic alone, on all three levels.

Notes, undo and hints

Pencil in what a cell could be, take back a slip, or ask for a hint that says why.

Picks up where you left off

Your puzzle and best times are saved on your device, no account needed.

How to play

Learn Sudoku in a minute

Fill the grid so every row, column and 3x3 box holds the digits 1 to 9 exactly once. No maths is needed, just clear thinking. It is free and ad-free, right in your browser.

Tap an empty cell, then tap a digit on the pad or press it on your keyboard.

A right digit stays. A wrong one turns red and counts as a mistake, so you can fix it at once.

Fill every cell to solve the puzzle. Solve it without hints to set a best time.

Start playing ↑

Rules

Sudoku rules

Three rules decide where a digit can go, and a few more decide what counts in this game.

Rows: Each row holds the digits 1 to 9 once each
Columns: Each column holds the digits 1 to 9 once each
Boxes: Each 3x3 box holds the digits 1 to 9 once each
Clues: The digits a puzzle starts with cannot be changed
One solution: Every puzzle has exactly one solution, and can be solved without guessing
Mistakes: A digit is checked as you place it. A wrong digit turns red and adds one to the mistake count; a right digit is locked in place
Best times: Each level keeps your fastest solve. A solve that used a hint does not set a best time

Controls

Controls and tools

The game is built for a phone first, and plays the same with a mouse or a keyboard.

Select: Tap or click a cell. Its row, column and box are tinted, and every cell with the same digit is highlighted
Digits: Tap a digit on the pad, or press 1 to 9. The small number under each digit shows how many are still to place
Notes: Turn on Notes (or press N) to pencil small digits into a cell. Holding a digit on the pad, or Shift with a digit key, does the same without switching. Placing a digit clears that note from its row, column and box
Undo: Takes back your last move, up to 60 moves back (U or Ctrl+Z). Mistakes already counted stay counted
Erase: Clears a wrong digit or the notes in a cell (Backspace or Delete)
Hint: Fills the selected cell, or the easiest next cell if the selected one is done, and says why when there is a simple reason (H)
Arrow keys: Move the selection around the board
Saving: A puzzle in progress is saved on your device, with its notes and undo history, so you can close the page and carry on later. The clock pauses while the page is hidden

Levels

Three levels

Every level uses the same rules. What changes is how many clues you get and which techniques you need to reach the solution.

Easy: About 38 clues. Singles are all you need
Medium: About 30 clues. Singles solve most of them; some also need locked candidates
Hard: 22 to 27 clues. Every hard puzzle needs more than singles and locked candidates: a naked pair or triple, a hidden pair or an X-wing

Strategy

Solving techniques

These are the techniques the puzzles are built around, from the easiest up. Together they solve every puzzle in the game.

For every level:

Hidden single: In a row, column or box, a digit that has only one cell left to go in belongs in that cell
Naked single: A cell where every digit but one already appears in its row, column or box takes the digit that is left

For medium and hard:

Locked candidates: When a digit's possible cells in a box all lie in one row or column, it cannot go anywhere else in that row or column. The same works the other way, from a row or column into a box

For hard:

Naked pair or triple: Two cells in a row, column or box that can only hold the same two digits keep those digits to themselves, so no other cell there can hold them. Three cells sharing three digits work the same way
Hidden pair: Two digits that can only go in the same two cells of a row, column or box leave no room for any other digit in those cells
X-wing: When a digit has the same two possible columns in two different rows, it must sit at opposite corners of that rectangle, so it cannot go anywhere else in those two columns. The same works with rows and columns swapped

FAQ

Frequently asked questions

Quick answers about Sudoku and how this version works.

Is Sudoku a maths game?

No. Sudoku is a logic puzzle. The digits are only nine different symbols, and no arithmetic is involved: letters or shapes would work just as well.

Do I ever have to guess?

No. Every puzzle has exactly one solution, and each is checked by a solver that uses only the techniques in this guide, with no guessing, before you see it.

What if I get stuck on a puzzle?

Use Notes to pencil in what each cell could be, then look for a single or a pair. If that does not help, Hint fills a cell and, when there is a simple reason, tells you what it is. A solve that used a hint does not set a best time.

Is my puzzle saved if I close the page?

Yes. A puzzle you have started is saved on your device, with its notes, mistakes, time and undo history, and is kept for 30 days.

Where did Sudoku come from?

The modern puzzle was designed by Howard Garns and first published in the United States in 1979 under the name Number Place. It became popular in Japan in the 1980s, where it was given the name Sudoku. Its idea goes back to Latin squares, which the mathematician Leonhard Euler studied in the 18th century.