Play Sudoku Online
Easy to expert puzzles with hints, notes and a fresh daily Sudoku.
How to Play Sudoku
Modes: Classic · Killer Sudoku · Daily
Sudoku is a logic puzzle played on a 9×9 grid, divided into nine 3×3 boxes. Some cells are prefilled.
Fill the grid so that every row, every column, and every 3×3 box contains the digits 1–9 exactly once.
Use the number pad (or keyboard 1–9) to place values, toggle notes, and get smart hints when stuck.
Rules
Each row, column, and 3×3 box must contain the digits 1–9 with no repeats.
A puzzle has exactly one solution — every move is deducible from the clues.
Scoring
| Complete | all cells correct |
| Solve time | tracked for your best |
History & Origins of Sudoku
Modern sudoku began in 1979, when American architect Howard Garns published “Number Place” in Dell Pencil Puzzles & Word Games. Japanese publisher Nikoli renamed it Sudoku in 1984.
The global craze arrived in 2004 when Wayne Gould’s puzzles appeared in The Times of London. Mathematicians estimate there are roughly 6.7 sextillion valid completed grids, and a well-made puzzle needs no guessing.
Common Mistakes to Avoid
- Guessing. A proper sudoku has exactly one logical solution; a lucky guess hides for many moves and then poisons the grid.
- Not writing candidates. Beyond Easy, holding every possibility in your head is why players stall.
- Only hunting cells. Half the deductions come from asking where a digit can go, not just what a cell can hold.
- Quitting a region after one scan. Every placement changes the board — rescan the box you just solved.
Tips & Strategy
Start with obvious singles — cells that can only hold one number.
Use notes to track candidates, then apply elimination across rows, columns, and boxes.
Look for naked pairs and hidden singles to break open harder grids.
In Killer Sudoku, cages must sum to their target with no repeats within the cage.
Frequently Asked Questions
- Is Sudoku free to play?
- Yes — Sudoku on ThinkyPlay is completely free, with no download and no sign-up.
- What difficulty levels are available?
- Play Easy, Medium, Hard, Expert, Master, or Extreme — each with a unique puzzle.
- Can I play Sudoku on my phone?
- Yes — tap cells and use the on-screen number pad. Works on any device.
- Who invented Sudoku?
- Howard Garns designed the modern puzzle in 1979 as “Number Place”. Japanese publisher Nikoli later named it Sudoku in 1984.
- Do I need to guess to finish hard puzzles?
- No. Correctly made Sudoku are fully solvable with logic — techniques like hidden singles, naked pairs and X-Wing replace guessing.