Classic Sudoku with AI-powered hints

How to play Sudoku

Sudoku is a logic-based number placement puzzle played on a 9×9 grid, divided into nine 3×3 boxes. The goal is simple: fill every cell so that each row, each column, and each 3×3 box contains all of the digits from 1 to 9, with no repeats.

No arithmetic is involved — it's pure logic. Every puzzle has exactly one correct solution, reachable through deduction alone.

Basic rules

• Each row must contain the digits 1–9, with no repetition.
• Each column must contain the digits 1–9, with no repetition.
• Each of the nine 3×3 boxes must contain the digits 1–9, with no repetition.
• The given clue numbers (pre-filled cells) are fixed and cannot be changed.

Step-by-step for beginners

1. Scan rows and columns first. Look at each row and column to see which digits are already placed. Any digit that appears in a row, column, and box eliminates itself as a candidate for all other cells in that group.
2. Find cells with only one candidate. If a cell has only one possible digit after scanning, fill it in. These are called "naked singles" and are the easiest starting points.
3. Use notes mode for harder cells. For cells with multiple candidates, use the notes feature to pencil in all possibilities. As you fill in other cells, come back and cross out eliminated candidates.
4. Look for hidden singles. Even if a cell has multiple pencilled candidates, check whether one of those digits can only go in that cell within its row, column, or box. If so, that's the answer.
5. Work box by box. Pick one 3×3 box and figure out where each missing digit can legally go. Often the row and column constraints narrow it down to one cell.
6. Use the AI hint if stuck. Tap the hint button and Sudoku AI will identify the next logical move and explain the technique used, so you learn the strategy rather than just getting the answer.

Difficulty levels

Sudoku AI offers four difficulty levels, each requiring progressively more advanced solving techniques.

Sudoku strategy tips

Naked singles

A naked single is a cell where only one digit is possible after eliminating all digits already present in its row, column, and box. Always scan for these first — they're free points and often unlock other cells.

Hidden singles

A hidden single occurs when a digit can only go in one cell within a row, column, or box, even if that cell appears to have multiple candidates. Scan each group for digits that have only one possible home.

Naked pairs

If two cells in the same row, column, or box share exactly the same two candidates and no others, those two digits must occupy exactly those two cells. You can safely eliminate those candidates from all other cells in that group.

Box-line reduction

If all candidates for a particular digit within a 3×3 box lie on the same row or column, that digit can be eliminated from the rest of that row or column outside the box. This is one of the most powerful basic techniques.

When to guess

A well-formed Sudoku puzzle never requires guessing — every cell can be solved through pure logic. If you feel stuck and tempted to guess, use the AI hint instead. It will point out the logical technique you may have missed.