Play Sudoku Online
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Keyboard: 1–9 to place, Backspace to erase, arrow keys to move, N to toggle notes.
Every puzzle is generated fresh and has exactly one solution, so it is always solvable by logic alone.
How to Play Sudoku
Fill the 9×9 grid above so that every row, every column, and every bold 3×3 box contains the digits 1 through 9, each exactly once. That’s the entire rule set — no arithmetic is involved. Every puzzle here has exactly one valid solution, reachable through logic alone, so you’ll never need to guess.
The only 3 techniques you need to start
Last Free Cell
A row, column, or box has eight of its nine cells filled. Whatever digit is missing from that group is the answer for the empty cell. This is the fastest win in Sudoku — always check for it first.
Last Possible Number
A digit can only fit in one cell of a box once you check its row and column too. Scan all three units together; if only one cell qualifies for that digit, it goes there.
Naked Single
After eliminating every digit that already appears in a cell’s row, column, and box, only one candidate is left. That’s the only number that can go in that cell.
Master these three and you can finish any Easy puzzle. For a full walkthrough with worked examples, read our Complete Beginner’s Guide to Sudoku.
Sudoku Puzzle Solving Tips
These are the habits that separate players who finish in ten minutes from players who stall halfway through. Use them in order — each one becomes necessary once the previous one stops producing progress.
- Start with the fullest row, column, or box. Fewer blanks means fewer possibilities to check, so you get quick wins that build momentum for the rest of the grid.
- Scan digit by digit, not cell by cell. Pick a number, find every place it already appears, then work out where else it can and can’t go. This is faster than staring at one empty cell trying to guess.
- Write pencil marks once scanning slows down. Note every candidate digit that’s still possible in each empty cell. This is standard practice at every skill level, not a beginner crutch.
- Re-check neighboring cells after every placement. A new number changes three units at once (its row, column, and box), and often unlocks the next cell immediately. Solving happens in waves, not one cell at a time.
- Switch perspective when you’re stuck. If row-and-column scanning stops working, switch to scanning box by box instead. A fresh angle almost always reveals something you missed.
- Look for pairs before you look for advanced patterns. If two cells in the same row, column, or box share the exact same two candidates, those two digits can be eliminated everywhere else in that unit. This alone unlocks most Medium puzzles.
- Never guess. Every properly built puzzle is solvable through logic alone. If you feel forced to guess, there’s a technique you haven’t spotted yet — not a flaw in the puzzle.
Sudoku Difficulty Levels Explained
Difficulty isn’t really about how many clues you’re given — it’s about which techniques are required to finish. A 30-clue puzzle can be easier than a 34-clue one if the clues are positioned well. Here’s what typically separates each level:
| Level | Typical clues | Techniques usually needed |
|---|---|---|
| Easy | 36–45 | Last free cell, last possible number, naked singles |
| Medium | 30–35 | Pencil marks, naked pairs, hidden singles |
| Hard | 26–30 | Pointing pairs, box/line reduction, naked triples |
| Expert | 22–26 | X-Wing, wings, unique rectangle, chains |
You can play all four levels right now using the difficulty selector at the top of this page — a fresh, uniquely-solvable puzzle is generated every time.
Common Sudoku Mistakes to Avoid
| Mistake | Fix |
|---|---|
| Placing a number without checking all three units | Always verify the row, column, and box before committing — missing just one causes silent errors |
| Trying to solve everything in your head | Switch to pencil marks the moment scanning alone stops working |
| Giving up on a stuck cell too quickly | Change your scanning angle — box-by-box instead of row-by-row, or vice versa |
| Guessing when nothing seems to fit | Every valid puzzle is logically solvable — look for a pattern you haven’t tried, don’t guess |
| Losing track of which numbers were “given” | Given clues are shaded differently on this board so you never confuse them with your own entries |
Quick Facts About Sudoku
- Sudoku uses digits 1–9 purely as labels — no math is ever required to solve a standard puzzle.
- There are exactly 6,670,903,752,021,072,936,960 valid completed 9×9 grids, and 5,472,730,538 that are essentially different from one another.
- The minimum number of starting clues for a puzzle with a unique solution is 17, proven mathematically in 2012.
- The modern puzzle was popularized worldwide after The Times of London began publishing it in November 2004.
- India is hosting the 19th World Sudoku Championship in Kolkata in October 2026 — read more in our complete guide.
Frequently Asked Questions
Do I need to be good at math to play Sudoku?
No. The digits 1 through 9 are just symbols — you could replace them with letters or colors and nothing about the difficulty would change. Sudoku is a logic puzzle, not an arithmetic one.
Is guessing ever necessary?
No. Every puzzle on this page is generated with exactly one valid solution, reachable through logic alone. If you feel stuck enough to guess, it almost always means there’s a technique you haven’t applied yet, not that the puzzle requires luck.
How long should an Easy puzzle take?
Most beginners take 15 to 30 minutes on an Easy puzzle. With practice using scanning and pencil marks, that typically drops under 10 minutes.
What’s the difference between this and other Sudoku sites?
Every puzzle is generated fresh in your browser using a solver that verifies uniqueness before the puzzle is shown to you — so you’re never stuck on a puzzle with multiple valid answers or no solution at all.