Sudoku Made and maintained by Brian Hamilton and Karan Hamilton.
Brian builds the playable puzzle tools, while Karan helps test clarity, difficulty feel, and the player experience.
Playable puzzles and controls are tested in the browser for rule accuracy, usability, and a clear solving experience. See how we make and test puzzles, our editorial standards, or report a problem.
Sudoku: The World's Most Popular Number Puzzle
Sudoku is a logic-based number-placement puzzle that has captivated millions of players across the globe. Despite involving numbers, it requires absolutely no maths — just patience, logical thinking, and pattern recognition. Whether you're picking up a sudoku puzzle for the first time or you're a daily solver, this page gives you everything you need: a free game to play right now and a complete guide to the rules, strategies, and history behind the world's favourite puzzle.
🤔 What Is Sudoku?
A standard sudoku puzzle consists of a 9×9 grid divided into nine 3×3 boxes (also called blocks or regions). Some cells are pre-filled with digits — these are the givens or clues. Your task is to fill every remaining cell so that:
- Each row contains the digits 1 through 9 exactly once.
- Each column contains the digits 1 through 9 exactly once.
- Each 3×3 box contains the digits 1 through 9 exactly once.
Every properly constructed sudoku puzzle has exactly one valid solution, and that solution can always be reached through logical deduction — no guessing required. That is worth backing rather than asserting. Our generator builds a full grid and then takes clues away one at a time, keeping a clue whenever removing it would leave the puzzle with more than one answer. A grid with two solutions can't reach you, because it is never allowed to exist. So when you get stuck, you are missing a deduction rather than needing to gamble — move to a different part of the grid and come back.
The Hint button is there for when that fails: it fills in one correct digit to get you moving again. It won't tell you why that digit was forced, so if you would rather learn the deduction than be handed it, the techniques below and our Blog & Tips walkthroughs are the better route.
Even though Sudoku uses numbers, it's not a maths puzzle! You could replace the digits with colours, shapes, or emojis and the rules would work exactly the same way. Your brain is practising logical reasoning, not arithmetic.
📋 How to Play Sudoku — A Step-by-Step Guide
If you're new to sudoku, here's a simple process to get started:
- Scan the grid — Look for rows, columns, or boxes that are nearly complete. If eight of the nine digits are already placed, the missing one is obvious.
- Use elimination — For each empty cell, ask: "Which digits are impossible here because they already appear in this row, column, or box?" The digits that remain are your candidates.
- Write pencil marks — Pencil marks (also called notes or candidates) are the small digits you write into a cell to track what is still possible there. Toggle Notes above the grid and tap a digit to add or remove it. Almost every technique past this point depends on having them, and on keeping them up to date.
- Look for naked singles — If a cell has only one candidate left after elimination, that must be the answer.
- Look for hidden singles — If a digit can only go in one cell within a row, column, or box, it must go there — even if that cell has other candidates.
- Repeat and refine — Each number you place narrows down the candidates elsewhere. Revisit rows, columns, and boxes until the grid is full.
Those first two steps are worth seeing rather than reading. Both grids below are one move from a placement, found without any technique more advanced than counting:
Start with rows, columns, or boxes that are almost full. If 8 of 9 digits are already placed, the last one writes itself! Also try focusing on one number at a time — ask "Where can the 5 go in this box?"
⭐ Sudoku Difficulty Levels Explained
This page offers six levels. The first four are generated to a fixed number of clues; the last two are drawn from banks of 5,000 puzzles each that we selected by how hard they are to solve, not by how few clues they carry.
| Level | What it asks of you | Clues |
|---|---|---|
| Easy | Scanning and naked singles. Nothing else required. | 40 |
| Medium | Hidden singles and basic candidate elimination. The everyday game. | 32 |
| Hard | Naked pairs, pointing pairs, box/line reduction. | 26 |
| Expert | X-Wing, Swordfish, XY-Wing and colouring. | 23–26 |
| Evil | Chains and long deductions. Curated, not generated. | 17–30 |
| Extreme | The hardest we publish. Expect to put it down and come back. | 21–27 |
Clue counts read from the generator and from the Evil and Extreme puzzle banks. Easy, Medium and Hard hit their target exactly; Expert aims at 22 but usually settles between 23 and 26, since a clue can only come out while the puzzle still has one solution. This page defaults to Medium; use the buttons above the grid to switch at any time.
This is the one thing almost every sudoku page gets wrong. Our Evil puzzles carry a median of 26 clues — exactly the same as Hard — and they are far harder. Difficulty comes from the techniques a grid forces you to use, not from how much of it starts empty. A 30-clue puzzle that needs a chain will beat a 22-clue puzzle that falls to hidden singles every time.
The fewest clues a valid sudoku can have is 17 — proved by exhaustive computer search in 2012. Two of the 5,000 puzzles in our Evil bank sit exactly on that limit.
🧠 Essential Sudoku Strategies and Techniques
Past Easy, you stop finding digits by counting and start finding them by ruling digits out. These are the techniques worth learning, roughly in the order they become useful. Each one has its own walkthrough with before-and-after grids:
| Technique | What it does | First useful at |
|---|---|---|
| Naked single | A cell with one candidate left. That candidate is the answer. | Easy |
| Hidden single | A digit that fits in only one cell of a unit, even if that cell has other candidates. | Easy |
| Naked pairs | Two cells in a unit sharing the same two candidates lock those digits away from the rest of the unit. | Medium |
| Hidden pairs | Two digits confined to the same two cells clear every other candidate out of them. | Medium |
| Pointing pairs | A candidate stuck in one row or column of a box is eliminated from the rest of that line. | Hard |
| Box/line reduction | The reverse: a candidate confined to one box within a line is eliminated from the rest of the box. | Hard |
| X-Wing | A digit in exactly two cells on each of two rows, sharing columns, clears that digit from those columns. | Expert |
| Swordfish | The same idea as X-Wing, stretched across three rows and three columns. | Expert |
| XY-Wing | Three two-candidate cells: a pivot that sees two pincers. Whatever the pivot holds, one pincer ends up on the shared digit, so it clears from every cell both pincers see. | Expert |
| Simple colouring | Follow a digit through units where it has exactly two homes, alternating two colours. If a colour appears twice in one unit it is false, and every cell of that colour can be cleared. | Expert |
"First useful at" is where our generator starts producing puzzles that need the technique — Easy and Medium grids are solvable without anything below the first two rows.
Always keep your pencil marks updated! When you place a number, immediately erase that candidate from all cells in the same row, column, and box. Stale notes are the #1 cause of mistakes in harder puzzles.
Beyond these, our Blog & Tips section covers the harder end — wings, chains, colouring and the fish family — with the same before-and-after treatment.
📜 A Brief History of Sudoku
The puzzle is younger than most people assume. American architect Howard Garns published it as "Number Place" in 1979; the Japanese publisher Nikoli picked it up in 1984, added the symmetrical-clue rule and the name Sudoku; and it went global in 2004 when Wayne Gould talked The Times of London into running one daily. Within a year almost every newspaper in the world had one. We cover the full story, including the Latin squares Euler was studying two centuries earlier, in the history of sudoku.
By 2005, Sudoku was dubbed "the Rubik's Cube of the 21st century". Today, an estimated 100+ million people solve Sudoku regularly worldwide. There are even World Sudoku Championships held annually since 2006!
💪 Benefits of Playing Sudoku
We are puzzle makers, not researchers, so here is the honest version. Sudoku reliably gives you three things: twenty minutes of undivided attention, steady practice at deduction and pattern recognition, and a task with a definite, satisfying end. Those are worth having on their own terms.
The bigger claims you see attached to puzzles — that they hold off cognitive decline, or raise IQ — are not ours to make. The research is genuinely mixed, and the honest summary is that you get measurably better at sudoku, with much weaker evidence that this transfers to anything else. Play it because it is a good way to spend twenty minutes.
If you want to actually get better rather than just play, stop when you get stuck and work out which deduction you were missing, instead of hitting Hint and moving on. Recognising the pattern next time is where the improvement comes from.
🎮 Sudoku Variations You Can Try
Once you've mastered the classic 9×9, why not explore other types of sudoku?
- 4×4 Sudoku — A smaller grid using digits 1–4 with 2×2 boxes. Great for kids and absolute beginners.
- 6×6 Sudoku — A medium-sized grid with 2×3 boxes. A perfect stepping stone to the full-size puzzle.
- Killer Sudoku — Cage-based sums replace the standard givens, blending Sudoku with Kakuro-style arithmetic.
- Jigsaw Sudoku — The regular 3×3 boxes are replaced by irregular jigsaw-shaped regions for a visual twist.
🚀 Tips for Faster Solving
- Start with the most constrained rows, columns, or boxes — Units with the most givens have the fewest possibilities, so they're easiest to crack.
- Focus on one digit at a time — Choose a number (say, 5) and scan the entire grid to see where it can and can't go.
- Always use pencil marks — Notes prevent mistakes and reveal patterns you'd miss otherwise.
- Don't guess — If you're stuck, switch to a different area of the grid or use our Hint button. Guessing often leads to errors that cascade.
- Practice daily — Speed comes from pattern familiarity, and familiarity comes from repetition.
🖨️ Printable Sudoku Puzzles
Prefer to solve on paper? Visit our Printable Sudoku section to download grids in all difficulty levels, or use the Sudoku Generator to create a custom PDF with your own difficulty, layout, and answer key. Each sheet is perfect for commutes, classrooms, or lazy Sunday mornings.