Select a difficulty and start playing!
1-9 Enter number
Backspace Clear cell
P Toggle pencil
How to Play
GoalFill the 9×9 grid so that every row, every column, and every 3×3 box contains the digits 1 to 9 exactly once.
Controls- Click a cell, then type a digit (1–9) to place it.
- Backspace / Delete clears a cell; Arrow keys move between cells.
- Press P to toggle Pencil mode and jot candidate notes for a cell.
DifficultyEasy gives more starting numbers; Expert gives very few, requiring advanced techniques.
Tips- Scan each row, column, and box for a number that can only go in one cell.
- Use Pencil mode to track candidates — then erase as you eliminate them.
- Look for "naked singles": a cell with only one possible candidate.
- Never guess — a valid Sudoku has exactly one solution you can reach by logic.
About Sudoku History, Strategy & Tips
Sudoku is a logic-based number-placement puzzle played on a 9×9 grid. The grid is divided into nine 3×3 boxes, and your goal is to fill every empty cell so that each row, each column, and each box contains the digits 1 to 9 exactly once. No maths is required — just pure deductive reasoning.
Here at 3D Protagon Puzzles you can play a fresh Sudoku every day, across four difficulty levels, right in your browser — no downloads, no sign-up required to play.
The History of Sudoku
Although Sudoku feels like a Japanese invention, its roots stretch back to 18th-century Switzerland, where mathematician Leonhard Euler developed Latin squares — grids in which each symbol appears once per row and column. The modern puzzle, with its 3×3 boxes, was designed by the American architect Howard Garns in 1979 and published under the name Number Place.
The puzzle found its huge audience only in 1984, when the Japanese publisher Nikoli introduced it in Japan under the name Sūji wa dokushin ni kagiru (“the digits must be single”), later shortened to Sudoku. A decade later, a British newspaper began printing daily Sudoku grids, and within months the craze had spread worldwide.
Solving Strategies
Scanning (beginner)
The first technique every solver learns is scanning. Pick a digit (say, 5) and scan each row, column, and box to see where 5 is already placed. Any empty cell that shares a row, column, or box with an existing 5 cannot hold a 5 — so by elimination you can often find the one cell in a box where 5 must go.
Naked and hidden singles
A naked single is a cell that has only one possible candidate left after you eliminate the digits already present in its row, column, and box. Use pencil marks (press P in our game) to track candidates. A hidden single is a digit that can only go in one cell within a row, column, or box — even if that cell has other candidates pencilled in.
Naked pairs and triples
If two cells in the same row, column, or box have exactly the same two candidates (e.g. both can only be 3 or 7), then 3 and 7 must occupy those two cells — so you can eliminate 3 and 7 from every other cell in that unit. The same logic extends to triples and quads.
Advanced: X-Wing and beyond
For Expert-level grids, techniques like X-Wing, Swordfish, and pointing pairs come into play. An X-Wing occurs when a candidate appears in exactly two places in each of two rows, and those places share the same two columns — letting you eliminate that candidate from the columns elsewhere. These patterns are hard to spot but immensely satisfying.
Sudoku FAQ
Do I need to be good at maths to play Sudoku?
No. Sudoku uses digits only as symbols — you never add, subtract, or calculate. It is a pure logic puzzle.
Is there always only one solution?
Yes. Every puzzle on this site has a single unique solution that can be reached by logic alone — you never need to guess.
What is pencil mode?
Pencil mode lets you jot small candidate numbers in a cell to keep track of possibilities. Press P to toggle it on or off.
How is difficulty determined?
Easier puzzles give you more starting numbers and require only basic scanning. Expert puzzles give you very few and require advanced elimination techniques.
Can I play on my phone?
Yes — the puzzle is fully responsive and works with touch input on phones and tablets.