Test with a solver

You can’t see a second solution by looking. You have to search for one. A solver is a program that does the search: it tries every possibility the rules allow and counts the answers it finds.

The count is all you need. One means the puzzle is sound. More than one means you need another clue. None means a clue contradicts the rules.

A solver can’t tell you whether the puzzle is fun. For that, you testsolve: someone else solves it without help and tells you where they got stuck.

Many setting tools can count solutions for you. On this site, the submit page runs our own solver on your puzzle before it lets you send it, and every imported puzzle is checked before it loads.

Whatever tool you use, count again after every change.

A testsolver tells you where they started, where they got stuck, and whether any step felt like a guess. If they had to guess, either the puzzle has a second solution, or a step needs a technique harder than you meant. Both are worth fixing.