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Hard Sudoku

Hard

Hard Sudoku trims the clues further. Look for hidden singles and box-line interactions before placing digits.

Time0:00
Difficulty

How to play

Click or tap a cell, then enter a digit. Use Notes for pencil marks. On desktop, arrow keys move the selection; press N to toggle notes.

Hard sudoku: scanning for hidden singles

What is Sudoku?

Sudoku is a logic puzzle on a 9×9 grid divided into nine 3×3 boxes. Each row, column, and box must contain the digits 1 through 9 exactly once. No arithmetic is required—only deduction.

How to play

  1. Scan for obvious singles—cells where only one digit fits.
  2. Use notes to track candidates when several digits might work.
  3. Check the row, column, and box together before committing a number.
  4. Reset restores the original puzzle; New puzzle shuffles a fresh grid.

Hard Sudoku tips

When the grid feels stuck, revisit boxes with only one or two empty cells. Pointing pairs from a box into a row can unlock the next placement.

Word tools

Need a break from numbers? Try the word unscrambler or anagram solver.

More Sudoku pages

Frequently asked questions

Is sudoku a maths game?
No. Sudoku only uses the digits 1 to 9 as symbols with no arithmetic involved. It is a deduction puzzle about placing each symbol exactly once in every row, column, and 3×3 box.
Do I need an account to play sudoku here?
No. Every sudoku grid on this site plays instantly in your browser with no signup, no download, and no saved profile. Notes stay on your device for the session.
What is the difference between the difficulties?
Easy grids can be solved with cross-hatching and singles. Medium introduces full candidate lists. Hard requires pairs and locked candidates, and expert adds box/line reduction and occasional X-wing patterns.
How does the daily sudoku work?
The daily sudoku is generated from the current UTC date, so every visitor sees the same grid until midnight UTC. It resets automatically and needs no account to play.

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