Most broken Nonograms come from one of six mistakes, and the biggest is filling a square before it’s certain. The others are slips: forgetting the gap between two blocks, reading a clue the wrong way, miscounting a long line, leaving empty squares uncrossed, and assuming which block a filled square belongs to. Each one is below, with how to spot it.
If you’re new, the rules and how to solve pages explain the ideas these mistakes go wrong on.
1. Filling a square before it’s certain
When a block could sit in two places, it’s tempting to pick one. Often the mistake shows at once: its own line can’t fit its clue any more. But not always. We took 100 of the game’s puzzles at each size, made the opening sweep, filled one square that should have been empty, and kept making honest moves until some line couldn’t match its clue:
| Size | Moves before a line breaks (median) | Still hidden after 10 moves | Longest |
|---|---|---|---|
| 5×5 | 0 (straight away) | 0 of 100 | 7 |
| 10×10 | 0 | 16 of 100 | 35 |
| 15×15 | 0 | 29 of 100 | 74 |
On a 15×15, nearly three wrong squares in ten go unnoticed for ten moves or more, and by then other squares have been filled because of them. Here’s one on a 10×10: a square in row 2, column 10 that should be empty.
Fifteen moves later, each one following honestly from the grid as it stood, column 5 can no longer match its clue of 2 4. It doesn’t even pass through the wrong square.
How to avoid it: only fill a square when every way the line could turn out agrees on it. If a block could still sit in two places, leave the line and work on the ones that cross it.
2. Forgetting the gap between blocks
Two blocks on the same line always have at least one empty square between them. Four filled squares in a row read as a 4, not as 2 2.
How to avoid it: when you finish a block, cross out the squares at both ends of it straight away. The gap is then on the grid, not in your head.
3. Reading a clue the wrong way round
Row clues read left to right and column clues read top to bottom, and the blocks appear in that order. A column with 1 3 has its single square above its 3, never below.
How to avoid it: say the clue in order as you place its blocks, “first the 1, then the 3”, and check the first block goes nearest the top or the left.
4. Miscounting a long line
On a 15×15, it’s easy to slip by one when counting where a block starts or ends, and a block one square out also throws off every column it crosses.
How to avoid it: use the darker line every five squares. Count from the nearest one, not from the edge.
5. Leaving empty squares uncrossed
Crosses aren’t decoration. A crossed-out square is what stops a block sitting there, and most techniques depend on it. We tried solving the game’s puzzles while recording only filled squares, never crosses, even using the strongest line-by-line reasoning. It got stuck on 75 of 100 5×5 puzzles, and on every one of 100 10×10s and 100 15×15s.
How to avoid it: whenever a line is finished, cross out the rest of it. Whenever a square can’t be filled, cross it. The game greys out a clue once its line matches, which is a good moment to check its empty squares are crossed.
6. Assuming which block a filled square belongs to
A filled square on its own doesn’t say which block it’s part of. In a row with the clue 1 3, a lone filled square could be the 1, or one end or the middle of the 3. Filling around it as if it were the 3 is a guess, however natural it looks.
How to avoid it: only work out which block a square belongs to when the others can’t reach it. The worked example on the how-to-solve page shows this done properly: a filled pair that can only be the 2, because a 1 can’t cover two squares.
How to recover from a mistake
- A line that can’t match its clue means a wrong square somewhere, often on a crossing line, and sometimes a long way back. Undo to the last move you were sure of.
- Press Stuck? It points out a wrong square before anything else, by naming its row.
- Stuck with no sign of a mistake? Cross out everything you know is empty, then look again at the lines that changed most recently. See when you get stuck.