To be completed, you will need to learn and use the advanced sudoku solving techniques. There are five : X-Wing, XY-Wing, simple colouring, swordfish and XYZ-Wing. Their number of uses is however limited in order to apprehend them gradually.
When you feel ready, you can then challenge yourself to an expert sudoku.
To solve an hard sudoku online, start by applying the basic techniques on the grid. Once all the opportunities are exhausted, you will then have to use one of the advanced techniques to unblock the situation :
This may allow you to directly place a number or give you new opportunities to use basic solving techniques.
Repeat this process to solve any free hard sudoku on our website.
Finished our daily hard sudoku ? Below are six more hard sudoku puzzles to solve online for free :