See why the next number belongs.
Enter the puzzle or the progress you made. Get a gentle hint, see the evidence, then apply a move you actually understand.
One deduction at a time.
A useful step does not always place a digit. It can remove a candidate, expose a pair, or reveal the only possible location in a box. The coach uses singles, locked candidates, pairs and X-Wing, with the actual cells highlighted as evidence.
A separate bounded search verifies whether the entered grid is unique, unsatisfiable or ambiguous. That answer is never used to invent explanations. If logical rules run out, you can choose a visibly labelled assumption-and-backtracking lesson.
Input, candidate notes and saved progress stay in this browser. No image recognition or third-party AI service is required.
What does “more than one solution” mean?
At least two different completed grids satisfy the digits you entered. A clue may be missing. The coach refuses to treat a digit taken from one arbitrary completion as logically forced.
Why does the lesson stop before the puzzle is complete?
The current set of human-style rules may not find the next move, even when the puzzle has a unique solution. This is a technique limit, not a claim that the puzzle is impossible. Search mode is optional and every assumption and reversal is labelled.
Can I enter a correct number in a different order?
Yes. Editing a non-clue cell starts from the actual board you now have and clears the old lesson. Analyze again to get a new path. Previous and next controls restore both values and candidate eliminations within a lesson.