Sudoku

Fill the grid 1–9 in every row, column, and 3×3 box. Three difficulties.

How to play Sudoku

Sudoku is a logic puzzle on a 9×9 grid divided into nine 3×3 boxes. Some cells start filled (the “givens”). Your job is to fill every empty cell with a digit from 1 to 9 such that:

Each row contains every digit 1–9 exactly once.
Each column contains every digit 1–9 exactly once.
Each 3×3 box contains every digit 1–9 exactly once.

Controls

Tap a number in the palette below the board to select it. The selected number is highlighted in yellow.
Tap an empty cell to place the selected number there.
To erase a number you placed, tap the cell first to highlight it, then tap it again (or use the “Erase” button).
Tap a filled cell (yours or a given) to highlight all peers (same row, column, and box) and all cells with the same digit.
Givens (the original puzzle numbers) cannot be edited.

Mistakes and the leaderboard

If a placement doesn’t match the solution, it appears in red and counts as a mistake. The mistake counter is shown at the top.

You can make up to 3 mistakes while still being eligible for the leaderboard.
From the 4^th mistake onward, the game continues but your time will not be uploaded to the public leaderboard.
Your local best on this device is also only updated for clean (≤ 3 mistake) wins.

Difficulty levels

Easy — 40 starting numbers. Most cells are constrained, easy to deduce step by step.
Medium — 32 starting numbers. Requires more reasoning across the whole board.
Hard — 26 starting numbers. Sparse; expect to use techniques like X-wing, swordfish, or naked pairs.

Strategy tips

Look for “singles.” A cell with only one possible digit (because all other 8 are forbidden by row/column/box) is a forced move.
Scan by digit. Pick a digit (say 7) and look for rows/columns/boxes that don’t have it yet. Often there’s only one place a 7 can go.
Use the palette counter. The small “{n}/9” under each digit tells you how many of that digit are already correctly placed. Numbers close to 9 are usually easier to finish.
Don’t guess on Hard. If you can’t see a forced move, look harder for techniques like “naked pairs” (two cells in a unit that can only contain the same two digits).

Where Sudoku came from

Although it feels quintessentially Japanese, the modern puzzle was designed in the United States. In 1979 it appeared in Dell magazines under the name “Number Place,” generally credited to the retired architect Howard Garns. A Japanese publisher, Nikoli, picked it up in the 1980s and gave it the name we know today — short for a phrase meaning roughly “the digits must be single.” The worldwide craze came later, in 2004–2005, when the puzzle began running in newspapers around the globe and turned millions of commuters into daily solvers.

Mathematically, a Sudoku grid is a special kind of Latin square, and a proper puzzle has exactly one solution. That single-solution rule is what makes the game fair: you should never have to guess. Every digit can, in principle, be reasoned out from the ones already on the board.

Solving techniques, from beginner to advanced

Naked single. A cell where eight of the nine digits are already blocked by its row, column, or box has only one option left. Fill it in.
Hidden single. Within a row, column, or box, a digit may have only one cell where it can legally go even if that cell could in theory hold other digits. This is the most common way to make progress.
Naked pairs. If two cells in the same unit can only contain the same two digits, those digits are locked to that pair and can be removed as candidates from every other cell in the unit.
Pointing pairs. When a digit’s only possible cells in a box all sit in one row or column, that digit can be eliminated from the rest of that row or column.
X-Wing & Swordfish. On Hard puzzles these column/row patterns let you eliminate candidates across the whole board. You rarely need them on Easy or Medium, but they are the key to finishing a sparse grid without guessing.

Frequently asked questions

Does every Sudoku have exactly one answer?

Yes. Every puzzle we generate is checked to have a single unique solution, so you can always solve it by logic alone — guessing is never required.

What happens if I make a mistake?

A wrong placement turns red and adds to your mistake counter. You can make up to 3 mistakes and still qualify for the public leaderboard and a new personal best; beyond that you can keep playing for fun, but the time will not be recorded.

Is Sudoku good for your brain?

Many people use it as a daily mental warm-up. It exercises pattern recognition, short-term memory, and patient step-by-step reasoning. It is not a cure-all, but it is a pleasant, screen-friendly way to keep those habits sharp.

Which difficulty should I start with?

Easy starts with 40 given numbers and can be solved with singles alone — ideal for learning. Move up to Medium once that feels automatic, and try Hard when you are comfortable spotting pairs and pointing patterns.

Offline play

Once this page has loaded, the game runs entirely in your browser. You can keep playing if you go offline. Scores you earn while offline are queued and uploaded automatically when you reconnect (only if logged in and within the 3-mistake limit).