How to Play Sudoku
Sudoku is a logic puzzle played on a 9×9 grid divided into nine 3×3 boxes. The goal is to fill every row, every column, and every box with the digits 1 through 9 so that each digit appears exactly once. Some cells are filled in at the start as clues — from these you deduce the rest of the solution using pure logic. Guessing is never required: every well-formed Sudoku has exactly one unique solution.
The most important beginner technique is the Naked Single: for any empty cell, check which digits are already present in its row, column, and box. Every digit that already appears in those three units cannot go in that cell. If only one option remains, fill it in immediately. When eight of nine digits are already placed in a unit, the ninth is forced automatically — this one observation alone clears a large portion of Easy-level puzzles.
The second foundational technique is the Hidden Single: a specific digit can only go in one cell within a row, column, or box — even though that cell may appear to have multiple candidates. Mastering these two techniques is enough to solve Easy and Medium puzzles completely without any further help. For Hard, Expert, and Master puzzles, advanced methods like Naked Pairs, Hidden Pairs, and X-Wing become necessary. Our built-in hint system explains the next logical step on demand — perfect for improving your skills without spoiling the puzzle.
5 Difficulty Levels – From Easy to Master
Difficulty is determined not just by the number of given clues, but primarily by the solving techniques the puzzle requires. Every puzzle is algorithmically verified to have exactly one unique solution.
- Easy – Many clues; almost every cell can be solved with Naked Singles alone. Ideal for newcomers or a relaxed break.
- Medium – Fewer given digits; Hidden Singles are occasionally needed. Good for players who know the basics and want a little more challenge.
- Hard – Requires systematic use of Naked Pairs and Hidden Pairs. Using the notes mode to track candidates pays off here.
- Expert – Demanding puzzles that need multi-step elimination strategies. For experienced players who want to sharpen their technique further.
- Master – For seasoned solvers only: minimal clues, maximum brainwork. These puzzles can occupy even experienced players for thirty minutes or more.
Free Online Sudoku – No Sign-up Required
Play directly in your browser — no download, no account, no hidden costs. The Progressive Web App saves your game state automatically via IndexedDB, so you can pick up exactly where you left off even after closing the tab or switching devices. You can also install the app on your home screen and use it like a native app, complete with full-screen mode.
Offline support means the game keeps running without an internet connection — perfect for the subway, a flight, or anywhere with patchy reception. Optional error highlighting marks incorrect digits in red so you spot typos instantly. The notes mode lets you pencil in multiple candidates per cell, just like solving on paper. The undo function lets you step back as many moves as you need — no penalty, no time lost.
The built-in timer shows how long you take on each puzzle and lets you chase your personal best across every difficulty level. All features — error highlighting, notes, hints, timer — are fully usable on small smartphone screens too.
Why Sudoku is Good for Your Brain
Sudoku trains logical thinking, concentration, and working memory — without any wasted screen time. Unlike many other games, there are no random elements: if you solve the puzzle, you earned it through pure reasoning. Regular Sudoku practice helps you recognise patterns faster, retain information in your head, and approach problems methodically — skills that prove useful far beyond the puzzle grid.
Research suggests that regular mental exercise can help maintain cognitive fitness over the long term. Sudoku suits all ages — from children practising logical thinking to adults keeping their minds sharp. Start with Easy, build confidence, and increase the difficulty as you notice yourself solving puzzles faster and with fewer hints.