Play Sudoku Online — Free Number Puzzle
Introduction
Sudoku is the number puzzle that conquered the world: a 9 by 9 grid where every row, every column and every 3 by 3 box must contain the digits 1 to 9 exactly once. The puzzle gives you a few starting digits and your job is to fill in the rest using pure logic. There is no arithmetic — only deduction — which is why it appeals to everyone from students to grandmothers. Play it free in your browser across five difficulty levels, with a notes mode for keeping track of candidates, and no download.
About Sudoku
Sudoku became an international phenomenon in the mid-2000s when newspapers discovered the Japanese puzzle and its elegant rules. The name is Japanese for "single number", but the puzzle itself was popularised in its modern form in the West. Its genius is that the rules fit in one sentence while the solving can take anywhere from minutes to hours.
Solving Sudoku is a pure exercise in elimination. Every empty cell can only hold a digit that is not already present in its row, column and box. Easy puzzles can be solved by scanning for cells with a single possible digit; hard ones require keeping track of candidates and testing chains of consequences. The notes mode on this page lets you write candidate digits in cells, exactly like pencil marks on paper.
This page uses the sudoku.js puzzle engine by Robert McGuire, released under the MIT licence, wrapped in an original interface designed for this site. The engine generates and validates puzzles across five difficulty levels, and the interface adds the notes mode and error checking that make digital sudoku more pleasant than paper. Everything runs in your browser with no download and no account.
How to Play Sudoku
Read the starting grid.
The puzzle begins with some digits already filled in. These are the clues — they are fixed and cannot be changed, and together they determine a unique solution.
Fill a digit into a cell.
Click or tap an empty cell and choose a digit. The digit is correct only if it does not already appear in that row, column or 3 by 3 box.
Use notes for candidates.
Before you commit, jot down the possible digits for each cell using the notes mode. This is the digital version of pencil marks and is essential for harder puzzles.
Follow the three rules.
Every row, every column and every 3 by 3 box must contain each digit from 1 to 9 exactly once. Satisfy all three and the puzzle is solved.
Choose your difficulty.
Start with an easy puzzle to learn the flow, then work up through medium, hard, very hard and insane as your elimination skills improve.
Sudoku Controls
| Action | Desktop | Mobile |
|---|---|---|
| Select a cell | Click a cell | Tap a cell |
| Enter a digit | Press 1 to 9 on the keyboard, or click the number pad | Tap a digit on the number pad |
| Toggle notes mode | Click the Notes button, then click a digit | Tap the Notes button, then tap a digit |
| Clear a cell | Press Backspace, or click the Erase button | Tap the Erase button |
| Undo last entry | Click the Undo button | Tap the Undo button |
| Restart the puzzle | Click the Restart button | Tap the Restart button |
| Choose difficulty | Select Easy, Medium, Hard, Very hard or Insane before starting | Select Easy, Medium, Hard, Very hard or Insane before starting |
| Fullscreen | Click the fullscreen button above the grid | Tap the fullscreen button above the grid |
| Exit fullscreen | Escape key | Tap the fullscreen button again |
Sudoku Tips & Strategies
Scan for single candidates first
Start by finding cells with only one possible digit — a digit missing from its row, column and box all at once. Filling these easy cells cascades into more singles.
Use notes early and often
Pencil in every candidate digit for a cell as soon as you can. The notes are not a crutch; they are the working memory of the puzzle, and harder puzzles are nearly impossible without them.
Check rows, columns and boxes together
A digit may fit a row and column but be blocked by its box, or vice versa. Always check all three constraints before you commit a digit.
Hunt for hidden singles
When a digit can only go in one cell of a row, column or box — even if that cell has several notes — it is a hidden single and it is forced. Find these before you resort to testing chains.
Look for naked pairs
If two cells in the same row, column or box both contain the same two candidate digits, those two digits cannot appear anywhere else in that unit. Removing them from other cells often unlocks the next step.
Work from the easiest unit
The row, column or box with the most filled digits is the most constrained and the easiest to solve. Attack the densest areas first and let them unlock the rest.
What makes Sudoku worth playing
- Sudoku across five difficulty levels from easy to insane
- Notes mode for keeping pencil marks in every cell
- Error checking that keeps your logic honest
- Runs entirely in your browser with no download or plugin
- Puzzle engine open source under the MIT licence with credit
Game Info
| Developer | Robert McGuire |
|---|---|
| Released | 2013 |
| Genre | Puzzle, Number, Logic |
| Players | Single player |
| Technology | HTML5 / JavaScript |
| Platforms | Desktop, Tablet, Mobile browser |
| Average session | About 15 minutes |
| Licence | MIT |
| Last updated |
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Sudoku — Frequently Asked Questions
Is Sudoku free to play?
Yes, completely. The puzzle engine is open source under the MIT licence and the game is free to play here with no payment, no sign-up and no premium version.
What are the rules of Sudoku?
Fill the 9 by 9 grid so that every row, every column and every 3 by 3 box contains the digits 1 to 9 exactly once. The starting digits are fixed and the puzzle has exactly one solution.
Can I play Sudoku on my phone?
Yes. Tap a cell and choose a digit from the on-screen number pad. The game works in portrait and landscape on mobile browsers.
What is the notes mode for?
Notes mode lets you write candidate digits into empty cells, just like pencil marks on paper. Keeping notes is the standard technique for solving harder puzzles.
How many difficulty levels are there?
There are five: Easy, Medium, Hard, Very hard and Insane. They differ in how many starting digits are given and how many advanced techniques are needed.
Do I need to be good at maths to play?
No. Sudoku uses no arithmetic at all — only the digits 1 to 9 as symbols. The challenge is logical elimination, not calculation.
What other number and logic puzzles are on this site?
If you enjoy Sudoku, 2048 is a faster number puzzle and Nonogram is a pure logic grid puzzle, both free in your browser with no download.
Licence & Attribution
Puzzle engine: sudoku.js by Robert McGuire · MIT License
Art and audio: Puzzle engine MIT (sudoku.js); the game interface is original to this site
Licence verified .