Difficulty and flow

A puzzle’s difficulty is mostly the hardest step it forces. A sudoku that falls to naked singles and hidden singles is easy. One that needs a naked pair somewhere is harder, even if every other step is a single.

Where the hard step sits matters too. A bottleneck is a point where the easy steps run out and the solver has to find something harder to go on.

Good flow means each step opens the next. The solver is never stuck for long, and the hard moment comes once, when it feels earned.

To make a puzzle easier, add a given that skips the hard step, then test that it is still unique. To make it harder, remove givens until the easy steps run out at the point you want, and check that the step you meant is the one that gets through.

Our hint system and walkthroughs name the technique for each step, which is a quick way to see where your bottlenecks are.

Call a puzzle easy only if a newcomer can finish it with the basic techniques. Players can rate every puzzle here on difficulty and fun, so a wrong label shows up quickly.