Sudoku Classic Online

Play free classic Sudoku online in your browser. Features 4 difficulties, daily puzzles, pencil notes, hints, undo/redo, and progress statistics.

How to Play Classic Sudoku

Sudoku is a logic-based combinatorial number-placement puzzle. The objective is to fill a 9×9 grid with digits so that each column, each row, and each of the nine 3×3 subgrids contains all numbers from 1 to 9.

No math or arithmetic calculation is required; the puzzle relies purely on logic, scanning rows and columns, and eliminating candidates.

Pro Strategies & High-Score Tactics

  • Look for rows, columns, or 3×3 boxes with 5 or more filled numbers to quickly narrow down missing digits.
  • Use Notes mode (pencil marks) to track candidates in difficult cells.
  • Look for Naked Singles — cells where only one number can logically fit.
  • Solve the Daily Sudoku puzzle every day to build up your winning streak.

Frequently Asked Questions

How do I enter pencil mark notes in this Sudoku game?

Click the Notes button (✏️) or press the N key on your keyboard to toggle Notes mode. When active, clicking digits 1-9 toggles candidate numbers inside the selected cell.

Is my game progress saved if I close or refresh the page?

Yes! Your board state, timer, mistake counter, and notes are automatically saved to your browser local storage every few seconds and resumed when you return.

What is the Daily Sudoku challenge?

The Daily puzzle generates a unique seeded board for each calendar day. Solve it once a day to increase your consecutive win streak.