Four difficulty levels, notes, hints, undo/redo, and a daily challenge. Every puzzle is solver-verified with exactly one solution.
Play Sudoku Online — Free Puzzle Game
Play free Sudoku online with unlimited puzzles, four difficulty levels, pencil notes, hints, and a daily challenge. Every board is solver-verified to have exactly one solution — no dead ends, no ambiguous guesses. Your progress, timer, and stats save locally in your browser with no sign-up required.
How to play
Choose Random, Continue, or Daily Challenge.
Select difficulty: Easy, Medium, Hard, or Expert.
Click a cell and enter numbers 1–9 using the pad or keyboard.
Use Notes for pencil marks and Hint when stuck.
Complete the grid with no repeats in any row, column, or 3×3 box.
Why play here?
100% free — no account, no download, no limits.
Four levels — Easy to Expert for all skill levels.
Smart tools — notes, hints, undo, redo, validate.
Daily puzzle — same challenge for everyone each day.
Private — everything runs locally in your browser.
Sudoku rules
Fill the 9×9 grid with digits 1 through 9.
Each row must contain all digits 1–9 exactly once.
Each column must contain all digits 1–9 exactly once.
Each 3×3 box must contain all digits 1–9 exactly once.
Difficulty guide
Easy — most starting clues, great for beginners.
Medium — balanced challenge for regular players.
Hard — fewer clues, needs careful deduction.
Expert — fewest clues, advanced logic required.
Tips to solve faster
Scan rows and columns for numbers that can only fit one cell.
Use Notes mode to track candidates in Hard puzzles.
Look for naked pairs and singles within 3×3 boxes.
Use Check Move before committing a risky guess.
Keyboard shortcuts
Arrow keys / WASD — move between cells.
1–9 — enter a number in the selected cell.
Works on desktop and mobile with touch controls.
Frequently asked questions
What are the rules of Sudoku?
Fill the 9×9 grid so every row, column, and 3×3 box contains digits 1–9 exactly once with no repeats.
Is every puzzle guaranteed to have a solution?
Yes. Every puzzle is verified with a solver to have exactly one valid solution before you play.
What is the difference between Easy, Medium, Hard, and Expert?
Difficulty controls how many starting clues remain. Easy has the most given numbers; Expert has the fewest and requires advanced deduction.
How do notes (pencil marks) work?
Turn on Notes mode and tap a number to add small candidate marks in a cell. Turn Notes off to place final answers.
Can I continue a game later or play a daily challenge?
Yes. Continue Saved Game picks up where you left off. Daily Challenge gives everyone the same puzzle each day.
Is this Sudoku game free?
Yes. ToolAdda Sudoku is completely free with unlimited puzzles and no sign-up required.
Is my progress uploaded anywhere?
No. Your board, moves, notes, and statistics are stored only in your browser's local storage.
How Hard Each Level Really Is
Every puzzle starts as a full, valid grid. The generator then removes numbers one at a time in random order and keeps a removal only if the puzzle still has exactly one solution; the level sets how many it removes. We generated 1,000 puzzles per level with this page’s own code and tried to finish each one with the two simplest techniques:
Naked single: a cell where only one digit fits its row, column and box.
Hidden single: a digit that has only one possible cell left in a row, column or box.
Clues and solving techniques needed at each difficulty level
Level
Clues given
Naked singles alone
With hidden singles too
Need a harder technique
Easy★
51 of 81
100%
100%
None
Medium★★
43 of 81
99.5%
100%
None
Hard★★★
35 of 81
80.6%
98.9%
1.1%
Expert★★★★
27 of 81 28 in 5 of 1,000
10.3%
68.8%
31.2%
The step from Hard to Expert is the big one: about a third of Expert puzzles need something beyond singles, such as pairs, which is where Notes earn their keep. Fewer clues usually means harder, but difficulty really depends on which techniques a puzzle needs, not only on how many numbers it shows. The fewest clues a proper sudoku can have is 17: in 2012 an exhaustive computer search showed that no 16-clue puzzle has a unique solution.