Sudoku generator

What the generator does

It builds a completed grid, then removes numbers one at a time. After every removal it checks two things: that the puzzle still has exactly one solution, and that it can still be solved by named techniques. It stops when the solving path costs what your chosen difficulty should cost.

That is why difficulty here means something. The generator has already solved every puzzle the way a person would before you see it.

Uses

• Worksheets for a class, with an answer key
• A booklet for a journey or a waiting room
• Puzzles for a newsletter, a parish magazine or a school newspaper
• Practice sets at one fixed difficulty while you learn a technique

Using the puzzles elsewhere

Puzzles you generate here are yours to print and hand out, including for a class, a club or a charity newsletter. See the terms for the detail.

How difficulty is decided

After each number is removed, the generator solves what is left using named techniques — singles, locked candidates, pairs, wings and fish — and adds up what that path costs. Removing another number usually makes the path more expensive. When the total reaches the band you asked for, the generator stops.

That is why a puzzle labelled hard here needs the moves a hard puzzle should need, rather than simply starting with fewer numbers than an easy one.

What the generator will not produce

• A puzzle with more than one solution — every removal is checked before it is kept.
• A puzzle that needs guessing — grids that cannot be finished by technique are discarded.
• A puzzle whose grade was assigned rather than measured.

Common questions