Frequently Asked Questions

Sudoku is a logic puzzle played on a 9×9 grid. The goal: fill every cell with the digits 1 to 9, so that every row, every column and every 3×3 box contains each of these digits exactly once. No calculation, no memorization — just logic.

Not at all. The digits could be replaced by letters or colors — it would work exactly the same. It's not an exercise in calculation, it's an exercise in reasoning. Many players who dislike math love sudoku.

With a 4×4 grid, you can start as early as age 4-5. 6×6 grids suit ages 7-8, and the classic 9×9 around age 10-12. It all depends on the child — the key is not to skip steps.

A row is a horizontal line (9 cells). A column is a vertical line (9 cells). A box is one of the nine 3×3 squares that divide the grid. Each of these three unit types must contain the digits 1 to 9, each exactly once.

A valid grid always has a unique solution. This is a construction rule. If a grid admits two or more solutions, it isn't considered a genuine sudoku. On Sudoku-Land, all our grids follow this rule.

It depends a lot on the level. An easy grid can be finished in 5 to 10 minutes. On hard or expert, expect 20 to 45 minutes, or even more. The site's timer gives you a good sense of your progress over time.

A common question. Playing regularly trains concentration, logic and patience. Studies suggest that reflection activities like sudoku may help maintain cognitive function with age — though it's not a medical guarantee.

Yes, and it's actually recommended if you want to improve. Sudoku-Land offers a daily puzzle refreshed every morning, the same for every player. It makes a great daily ritual.

On Sudoku-Land, mistakes appear in red as soon as you enter an incorrect digit. If every cell is filled with no red, the grid is complete and won. On paper, check that every row, column and box contains the digits 1 to 9 without repetition.

It's not (only) the number of digits given at the start. It's mostly the complexity of the logical techniques needed to solve the grid. On easy, simple observation is often enough. On expert, you need to chain reasoning across several cells at once.

Not always. A grid with lots of digits can remain very hard if their placement forces complex deductions. Conversely, some grids with few digits solve almost by themselves. It's the type of logic required that determines difficulty, not the quantity.

Start with Easy. You'll learn the basic mechanics without getting discouraged. Once you solve easy grids without much hesitation, move to Medium, then Hard. Don't skip steps — a natural progression is much more enjoyable.

Four levels: Easy, Medium, Hard and Expert. These are the classic four levels found in most sudoku apps and books. Each level corresponds to a specific set of logical techniques.

Absolutely. Moving from Medium to Hard is often the toughest jump. That's where you need to learn the first advanced techniques — notably using notes (candidates). Our "How to play" page explains it all.

Three concrete tips: play regularly at the same level until you feel comfortable. Learn notes mode — it's the turning point for many players. And read the techniques on our "How to play" page — each technique you unlock opens up new grids.

For well-built grids — easy, medium, hard — yes. A valid grid can always be fully solved through logic. On expert, some configurations require advanced techniques that can look like guesswork, but it's rigorous logic, not chance.

The software that generates the grids simulates human solving and measures the techniques required. The more advanced the techniques, the harder the grid is rated. On Sudoku-Land, levels are calibrated to match players' actual experience.

Four formats: 4×4 (Kids Sudoku), 6×6 (Junior Sudoku), 8×8 (Junior+ Sudoku) and the classic 9×9. Each has its own box rules and its own level of complexity.

The 4×4 is ideal for understanding the rules without pressure. Once the mechanics click, move to 6×6, then 9×9. It's also the recommended order for kids learning the game.

A 4×4 grid, divided into 4 boxes of 2×2. It uses the digits 1 to 4. It's more colorful, more visual, with bigger cells. Designed to be playable from age 4-5, but even adults new to sudoku find it interesting.

Not necessarily. The 8×8 (with 2×4 boxes) is an original variant that can be confusing at first because of its rectangular box shape. But in terms of pure logic, the 9×9 remains richer and more complex.

Because a 6×6 grid can't be divided into equal squares with 6 cells each — mathematically impossible. So it uses 2×3 boxes (2 rows, 3 columns). It's a mathematical constraint, not an arbitrary choice.

The principle is identical for every size: every row, column and box must contain each digit exactly once. Only the grid size, the number of digits used and the shape of the boxes change.

Yes. All the grids on Sudoku-Land are completely free, no sign-up and no limit on the number of games.

Yes. Even with only 4 digits, a 4×4 grid on "Hard" mode can require the same logical reasoning as a 9×9. Fewer cells doesn't mean less thinking.

It lets you pencil in every digit that could possibly fit in a cell — just like on paper. It's essential for hard and expert grids. Turn it on with the "Notes" button or the Space key.

It reveals the correct value for a selected cell. You get 3 hints on Easy and Medium, 2 on Hard, 1 on Expert. Use them sparingly — once used up, that's it for the current game.

When you click a cell, a circle of buttons appears around it showing the available digits. It's especially handy on mobile, avoiding the need to navigate to the numpad. You can turn it on or off with the "Ring" button.

Yes. Use the 1–9 keys to enter digits, arrow keys to move between cells, Delete or Backspace to erase, Space to toggle notes mode, and Ctrl+Z to undo.

It tracks the last 20 actions. If you entered a wrong digit or accidentally deleted a note, you can step back as many times as needed within that limit.

It places the numpad to the right of the grid instead of below it. Handy on large screens or in landscape mode on tablets. The site also switches to side mode automatically when your screen is wider than it is tall.

Click the moon 🌙 icon in the top right. To switch back to light mode, click the sun ☀️. Your choice is remembered for future visits.

Yes. The interface adapts to every screen size. On mobile, the selection ring is especially handy for entering digits without needing to aim for a small numpad.

Yes, with the ⏸ button next to the timer. The timer stops and the grid is hidden. Click ▶ to resume.

Each digit has its own pastel color to make the grid easier to read. It's not just decorative — visually spotting a digit among others is faster when each has a distinct hue.

Yes. After every move, your progress is saved in the browser. If you close the tab or shut down your computer, you can resume exactly where you left off on your next visit.

7 days. After that, the game is deleted automatically. If you want to resume an old game, don't wait too long.

No. All saves and stats are stored locally in your browser (localStorage). Nothing goes through a server. Your data stays with you.

Yes. Your save is tied to your browser on your device. If you switch from Chrome to Firefox, or from your PC to your phone, you start from scratch.

In the "My stats" section at the bottom of the game page, there's a "Reset stats" button. It clears all locally stored stat data.

It's the number of consecutive games won. If you lose a game or don't finish it, the streak resets to zero. A good indicator of consistency.

The "Sudoku 9×9" page (random games) and the "Daily puzzle" page share the same statistics. This is intentional — they use the same grid type, so it makes sense to combine the data.

Every day, a new grid is offered to every player on the site. Everyone plays the same grid on the same day — a bit like a newspaper sudoku. It changes daily at midnight.

The system selects a grid based on the day and month. The day/month combination determines both the grid and a geometric transformation applied to it (rotation, mirror…). This produces 372 unique combinations per year.

Yes, that's the Print page. Choose the level, the number of grids per page (1, 2 or 4) and the number of pages. The layout is optimized for A4 printing.

Click "Print / PDF". In your browser's print dialog, choose "Save as PDF" as the destination. Select A4 format, portrait, and uncheck headers/footers for a better result.

Yes. A "Show solution" toggle lets you print a mini solution under each grid. Handy if you're printing for someone who doesn't want to get stuck.

Yes. Every click on "New grids" pulls different grids from our database. You'll never see exactly the same combination twice.

Yes. Four levels are available for printing: Easy, Medium, Hard and Expert. You can also mix them by generating multiple times.

First look for units that are almost full — rows, columns or boxes with only 2 or 3 empty cells. The fewer possibilities remain, the easier it is to find the missing digit. Start with the obvious before hunting for complex patterns.

It's when, in a row, column or box, there's only one cell left where a given digit can go. Even if that cell seems to have several possibilities at first glance, it's the only option for that digit in that unit.

A cell that has only one possible candidate left. Every other digit has been eliminated because it already appears in the same row, column or box. It's the most direct deduction in sudoku.

Two cells in the same unit that share exactly the same two candidates. Since these two digits are "reserved" for those two cells, you can eliminate them from every other cell in the unit. Very useful starting from Hard level.

Yes, it's nearly essential. On easy, you can often solve "in your head". On hard and expert, noting the candidates in each cell is the only way to spot the logical patterns that unlock the situation.

When, within a box, a candidate digit can only be placed on a single row (or column), that digit becomes impossible elsewhere on that same row outside the box. You then eliminate that candidate from the other boxes on that row.

An advanced technique. If a digit appears in only two cells on each of two different rows, and those cells are in the same columns, the digit cannot appear elsewhere in those two columns. You eliminate it from every other cell in those columns.

Human players naturally start with the boxes (visually delimited zones), then rows, then columns. It's the most intuitive order. After a few games, you'll develop your own method.

No, not for well-built grids. Everything can be solved through logic. If you find yourself needing to "try" a digit without logical certainty, it's often because a technique still eludes you — not that the grid is impossible.

On Sudoku-Land, mistakes appear in red as soon as you make them. If the grid shows no error but you can't find another move, you're stuck — time to learn a new technique or use a hint.

Sudoku as we know it was popularized by Japanese publisher Nikoli in 1986, but its origins trace back to a 1970s American puzzle called "Number Place". Wayne Gould, a retired New Zealand judge, introduced it to the world press in the early 2000s by convincing the Times of London to publish it.

It's nuanced. The basic mechanics come from the United States (Dell Magazines, 1970s). Japan adopted it, refined it and made it popular under the name "Sudoku" (数独, "single numbers"). The worldwide explosion dates to 2004-2005, driven by the British press.

Mathematicians have calculated that exactly 6,670,903,752,021,072,936,960 distinct complete grids exist. Removing those equivalent by symmetry or rotation, 5.4 billion truly distinct ones remain. Enough to play for a very long time.

17. Japanese enthusiasts have discovered grids with only 17 given digits that have a unique solution. With 16 digits, uniqueness cannot be guaranteed — it's mathematically proven.

Yes, in the computer science sense. Solving a generic sudoku (of size n²×n²) is an NP-complete problem — there's no universal instant algorithm for every possible grid size. But for the standard 9×9, a computer solves it in milliseconds.

A puzzle made of five overlapping 9×9 grids, forming a cross-shaped structure. Solving the grids is interconnected — the cells shared between two grids must satisfy both grids' constraints. Reserved for very experienced players.

Partly because the complexity of Japanese characters made creating crosswords at scale difficult. Number-based sudoku became the ideal logical alternative for the Japanese press. It filled the gap left by the lack of large-scale crosswords.