Pick a difficulty, enter numbers with keyboard or touch, and print the current puzzle whenever you want.
An expert Sudoku begins with only around 26 clues and ranks among the hardest puzzles there are. Almost every cell starts with several candidates, and without consistent notes you will barely move forward. This level is made for seasoned solvers who handle advanced techniques confidently and can sustain long chains of elimination. An expert puzzle can take thirty minutes or more.
With so few clues there are barely any safe cells at the start. You have to note every candidate systematically and then recognise patterns that link several units at once. Patience and a clean note system matter more here than speed.
At expert level you need techniques such as X-Wing, Swordfish and XY-Wing. Swordfish extends the X-Wing idea across three rows and columns. XY-Wing uses three linked cells with two candidates each to eliminate a number elsewhere. These patterns solve positions where simpler techniques fail.
Expert Sudoku rewards a calm, methodical approach. Never tackle a cell by guessing; a single wrong entry can make the whole puzzle unsolvable. Keep your candidates up to date and rely on the advanced patterns to solve even the toughest grid with pure logic.
Start with an easy Sudoku. Focus first on rows, columns and 3x3 boxes that already contain many digits, because those usually reveal the next safe move fastest.
Move to another area of the grid and compare row, column and box again. It also helps to use notes for candidates instead of guessing.
Easy puzzles start with more given numbers and shorter logic chains. Harder levels provide fewer clues, so solving them requires more careful deduction and longer sequences of reasoning.