Play free online Sudoku with six difficulty levels — Easy to Extreme. No login, no download. Pick your difficulty and start solving.

What is Sudoku?

Sudoku is a logic-based number puzzle played on a 9×9 grid divided into nine 3×3 boxes. The goal is simple: fill every row, column, and box with the digits 1 through 9, with no digit repeating in any row, column, or box. Despite relying purely on logic — no maths required — Sudoku offers a satisfying challenge at every skill level.

How to play

Choose a difficulty — start with Easy to learn the patterns, then progress to Expert or Extreme for a real challenge.
Select a cell and tap a number on the pad to fill it in.
Use Notes to pencil in candidate digits when a cell has more than one possibility.
Use Hint (up to 3 per game) if you get stuck — it reveals one correct digit.
Avoid 3 mistakes — the game ends if you place three wrong numbers.

Every puzzle has exactly one solution, reachable by logic alone. Read our Sudoku strategy guide to learn techniques like naked singles, hidden pairs, and X-wings.

What makes Sudoku Zen different

Most online Sudoku sites wrap a decent puzzle in a terrible experience: sign-up walls, streak reminders, video ads between games. Sudoku Zen is built around the opposite idea — the board loads in under a second, works offline, and remembers your game locally in your browser, so you can close the tab mid-puzzle and pick it up later. Every board is generated with a solver that verifies a unique solution and rates its true difficulty by which techniques it requires, not just by how many clues are removed. That means a Hard board here actually needs Hard techniques — pairs, pointing pairs, box/line reduction — and an Extreme board will make you work for every cell.

What the difficulty levels mean

Easy and Medium boards can be solved with singles alone — scanning rows, columns and boxes for the only cell a digit can go. Hard introduces candidate work: you'll want Notes on, and techniques like naked pairs and hidden pairs start to matter. Expert and Master demand chained deductions — pointing pairs, box/line reduction, triples. Extreme is for solvers who enjoy staring at a board for a long minute before the single available move reveals itself. If you're not sure where you stand, start on Medium: it's the level where the game starts teaching you to see patterns instead of testing digits.

A very short history

Modern Sudoku descends from Leonhard Euler's 18th-century Latin squares, but the puzzle as we know it was published as "Number Place" in a 1979 American puzzle magazine, refined in Japan in the 1980s (where it got the name sūdoku, "single number"), and exploded worldwide in 2004–2005 when newspapers began printing it daily. It's now the most played logic puzzle on Earth — a fifty-year-old design that has never needed a redesign, which is exactly the kind of game we like.

Frequently asked questions

Can every puzzle really be solved without guessing?

Yes. Every board is checked by our generator to have exactly one solution reachable through logical deduction. If you're stuck, it's a technique you haven't spotted yet — not a coin flip. The strategy guide covers eight techniques with diagrams.

Does it work offline?

Yes. The game is a Progressive Web App: after your first visit it's cached in your browser, so it loads and plays with no connection — on a plane, on the metro, anywhere.

Is my progress saved?

Your current game, statistics and settings are stored locally in your browser. Nothing is sent to a server and no account is needed — which also means clearing your browser data clears your progress.

Why only three hints?

Hints are a ladder, not an elevator. Three per game is enough to get unstuck without turning solving into watching. If you're using all three every game, drop one difficulty level — you'll improve faster.