Sudoku is a logic puzzle where you fill a 9×9 grid so every row, column, and 3×3 box contains the digits 1–9 exactly once.

Do I ever need to guess?

No. Every puzzle is guaranteed solvable through pure logic. The hint system shows you the logical path when you are stuck.

What are pencil marks?

Small candidate digits you can write in empty cells to track which numbers are still possible. Essential for advanced techniques.

Sudoku

Solve with logic. Learn real techniques. No guessing required.

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Pencil mode

Error highlight

Auto candidates

Tap a cell, then tap a digit below — or press 1-9 on keyboard.

How to play Sudoku

Fill every cell of the 9×9 grid so that each row, each column, and each of the nine 3×3 boxes contains all digits from 1 to 9 exactly once. Click or tap any empty cell to select it, then press a digit key or tap a digit in the palette to place it. Use Pencil mode to write small candidate digits in a cell when you haven't decided yet — they auto-clear when the cell is filled by any constraint.

The three-tier hint system teaches real Sudoku technique names as you play. Tier 1 softly highlights the cell with the easiest next move. Tier 2 draws constraint rings showing which cells limit the candidates. Tier 3 reveals the full technique explanation — names like Naked Single, Hidden Pair, and X-Wing so you can recognize them next time without help.

Difficulty levels are calibrated to the logical techniques required: Easy uses only singles; Medium adds pairs; Hard adds triples and pointing patterns; Expert requires X-Wing or more advanced logic. Every puzzle has exactly one solution and is solvable through logic alone. Game stats and streaks are stored locally on your device.

Quick guide

Use cases, answers, and nearby tools

Compact below-tool notes that help first-run users and repeated visitors move faster without changing the main interface.

Chinese search: 數獨、數獨線上、數獨解題、數獨技巧

How to use

Run a clean first pass

Select a difficulty and tap New Game to start a fresh puzzle.
Tap a cell, then tap a digit in the palette or press a number key to place it.
When stuck, use the three hint tiers — each reveals more about the logical technique needed.

Examples

Real jobs this page helps with

Learn solving techniquesUse the Tier 3 hint to learn technique names like Naked Single and X-Wing — then try spotting them yourself next game.
Track your improvementThe post-solve heatmap shows your fill order so you can see how your solving strategy evolves over time.

FAQ

What people usually want to know

What is Sudoku?: Sudoku is a logic puzzle where you fill a 9×9 grid so every row, column, and 3×3 box contains the digits 1–9 exactly once.
Do I ever need to guess?: No. Every puzzle is guaranteed solvable through pure logic. The hint system shows you the logical path when you are stuck.
What are pencil marks?: Small candidate digits you can write in empty cells to track which numbers are still possible. Essential for advanced techniques.

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