A useful nonogram hint should explain why a mark follows from the clues. In Nonogram Online, the next move comes from checking legal placements, or, when needed, checking whether an assumption can lead to any complete solution. A separate mistake check runs first and compares your existing marks with the stored answer.
Those are different kinds of help. This article explains both, using a small example you can verify before trying the playable Arrow puzzle.
First comes a mistake check
When you press Hint, the game checks your filled and empty marks against the puzzle's stored solution. If a mark disagrees, it points you to a row to check and stops before adding a new square.
That message helps prevent a wrong assumption from generating more wrong marks. It is not a deduction obtained solely from the row's visible clue. The stored answer is used for this preliminary check.
A local row can still have legal placements even when one of its marks disagrees with the complete puzzle. That is why an answer-based mistake warning can appear before you see an obvious contradiction yourself. Our empty-cell mistakes example shows how a plausible row can lead you astray.
A line hint compares all legal placements
Once the marks pass the mistake check, the deduction function receives the board, its size, and the row and column clues. It enumerates placements that fit each line's clues and existing marks.
For a five-cell line with clue 3 and no marks, the possibilities are:
| Placement | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|
| 1 | ■ | ■ | ■ | × | × |
| 2 | × | ■ | ■ | ■ | × |
| 3 | × | × | ■ | ■ | ■ |
3 legal placements. ■ filled; × empty. These rows are alternatives, not consecutive moves.
Every placement fills position 3. A hint can therefore prove that cell filled without selecting a favourite placement or copying a cell from the answer picture.
Now suppose crossing clues have proved both outer cells empty:
| Placement | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|
| 1 | × | ■ | ■ | ■ | × |
1 legal placement. ■ filled; × empty. These rows are alternatives, not consecutive moves.
Only one placement remains. Any unknown middle square must be filled. The explanation can say that only one arrangement fits the clue and your marks. If several arrangements remain, it can instead say that they all agree on a particular cell.
The same reasoning can prove an empty cell: if none of the remaining placements fills a position, that position must be empty. Hints do not only add filled squares.
One proved square is not a complete solution
The interface applies one square per hint. It may choose a deduction from another line before the one you were inspecting. The current implementation favours lines with fewer possible placements; at equal counts, it prefers a filled-cell deduction over an empty-cell deduction.
Several squares may already be forced in a line even though the hint records only one. After reading the explanation, try to identify another square that follows for the same reason. That turns the hint into a starting point for your own reasoning.
On a fresh Arrow puzzle, row 3 has clue 5. Ask for a hint and compare the message with that full-line rule. If you have saved progress, the next hint may differ. Restart only if you want to clear that puzzle and repeat the fresh-board example.
When a single line is not enough
If line-by-line reasoning produces no move, the hint engine considers an undecided square in two ways: filled and empty. For each assumption, it searches for a complete board that satisfies all row and column clues and existing marks.
If one assumption admits no complete solution and the other does, the square is forced. The on-screen explanation says that the opposite choice would make the full set of clues impossible.
This is proof by eliminating an impossible case, rather than asking the player to commit to a random guess. However, the short hint message does not display the entire search tree. It gives the conclusion and the kind of reasoning used, not a complete human-readable account of every branch. Our longer 15×15 walkthrough provides step-by-step line evidence for a published example instead.
Unique does not mean easy
A puzzle has a unique solution when exactly one complete board matches all its clues. That fact does not tell you whether the next move is obvious, whether simple overlaps will solve every stage, or how difficult a person will find it.
The site's puzzle checks verify unique solutions. The hint engine can use reasoning beyond a single-line overlap. We therefore describe these as different properties rather than promising that every puzzle is solvable using only beginner techniques.
Grid size is also only one part of difficulty. A full row in a large grid may be easy, while a smaller grid with several competing placements can require more careful reasoning.
Use a hint as a question to answer
Before pressing Hint, name one line you think is promising and explain what you have tried. After the hint appears, ask:
- Was this a mistake warning, a line-placement deduction, or a whole-grid contradiction argument?
- Which existing marks did the reasoning depend on?
- Can I make another move with the same reason?
If it is a mistake warning, repair or undo the unsupported mark first. If it is a line deduction, compare the placements yourself. If it is a whole-grid argument, recognise that the short message may not teach you the full proof.
You can undo a hint if you want to repeat its reasoning manually. For a guided introduction without relying on hints, follow the complete 5×5 example or the stuck-check routine.