Each row, column and 3 by 3 box holds the digits 1 to 9 one time. Fill the grid as fast as you can.
Your best – 3 mistakes end the run
or press Space
Type a digit in the selected cell. N notes, Z undo, Backspace erase
Rules & what counts
Hard Sudoku: Play Free Online
A hard Sudoku on the classic 9 by 9 grid. Each row, each column and each 3 by 3 box must hold the digits 1 to 9 one time.
A hard puzzle starts with 24 to 29 digits. At least one step needs an advanced technique: a naked triple, an X-wing or an XY-wing.
The server deals a new puzzle for every run and keeps the answer. Every puzzle has one solution and falls to logic alone. Your result is your time to the last correct digit.
How to play
Select Start. The clock starts when the grid shows.
Click or tap an empty cell, then a digit on the number pad. On a keyboard, type the digit.
Use Notes to write the candidates of a cell. The advanced techniques work on the candidates.
A wrong digit turns red and counts as a mistake. The third mistake ends the run, and the run is not saved.
Select Erase to clear a cell, or Undo to take back the last entry.
What counts in this quiz
Your result is the time from the moment the grid shows to the moment you enter the last correct digit.
On the leaderboard, a shorter time ranks higher.
A run that ends with three mistakes is not saved.
What's not included, and why
The clock does not stop when you leave the page or change tabs.
There are no hints.
A run under 90 seconds is not saved.
Good to know
An X-wing: when a digit has only two places in each of two rows, and those places are in the same two columns, the digit leaves every other cell of those columns.
An XY-wing uses three cells with two candidates each. One of the two outer cells must hold the shared digit, so that digit leaves every cell that sees both.