The idea in one sentence
You never guess. You look at one line at a time, ask “which cells are filled in every possible arrangement of this clue?” and “which cells are empty in every arrangement?”, and mark only those. Each answer gives the crossing lines new information, and the picture builds up line by line. Everything below is a different way of answering those two questions quickly.
If you need the rules first, they are in What Is a Nonogram?.
Step 1: Clear the easy lines
Some lines solve themselves before you think. A clue of 0 means the whole line is empty: cross it out. A clue as long as the line means every cell is filled. And when the runs plus the single gaps between them add up to the full length, there is only one way to place them.
Scan every row and column for these first. They cost nothing and they often hand you the first foothold on the board.
Step 2: The overlap method
This one technique solves more cells than all the others together. Take a single run and slide it as far left as it can go, then as far right. The cells it covers in both positions must be filled, wherever the run really is.
There is a shortcut. Work out the line's slack: its length minus the sum of the runs minus the gaps between them. Any run longer than the slack fills run length − slack cells in its middle. In the example the slack is 10 − 7 = 3, so a run of 7 fills 4 cells. A run of 3 in that same line would fill nothing, because it is not longer than the slack.
Step 3: Overlap with several runs
The same idea works when a line has more than one number. Push all the runs to the left together, then all to the right, and compare each run with itself. Because the slack is shared by the whole line, a tight clue fills cells in several places at once.
Start with the lines that have the least slack — usually the ones with the biggest numbers. On a fresh board this is how you find your first filled cells.
Step 4: Work from the edges
A filled cell near the edge of the grid is a strong clue. The first run of the line has to cover it, and the wall stops that run from sliding further away, so the run is pinned close to the edge.
The same goes for an X next to the wall: a run cannot start in a crossed-out cell, so it is pushed inwards, and the overlap grows.
Step 5: Cross out what no run can reach
Filled cells tell you where runs are; they also tell you where runs are not. Once you know one cell of a run, the run can only stretch so far from it. Everything beyond that reach is empty.
And when a line already shows every run its clue asks for, the rest of the line is empty. Cross it out straight away: those X marks are exactly what the crossing columns need.
Step 6: Let rows and columns trade information
No single line solves a whole puzzle. The trick is the loop: every cell you mark in a row is also a new fact for a column, which may now give way, which gives a new fact to another row. Solvers keep going round that loop until nothing changes.
Here is a complete 10×10 puzzle solved exactly that way. Each press of Next step takes the next line that has something new to say, applies only what is certain, and tells you what changed. No step ever guesses.
Notice how often the first steps come from the longest clues, and how the X marks from one line keep unlocking the next. That rhythm is the same on a 60×60 board.
Big boards: 30×30 to 60×60
Large nonograms use exactly the same logic; they just give you more lines to keep track of.
- Do a full overlap pass first. Go through every row, then every column, with Step 2 and 3 only. On a big board that alone can fill a fifth of the picture.
- Mark X generously. On a 50×50 grid you cannot hold the empty cells in your head. The marks are your memory.
- Finish regions. When an area around a long run settles, complete it before moving on — it gives clean edges to the lines that cross it.
- Use the clue sums. A line whose runs leave very little slack is worth rereading every time one of its cells changes.
- Take breaks. Progress saves after every move, so a 50×50 can be an evening project rather than a sprint.
Ready for one? Our 50×50 nonograms are checked by the solver to need no guessing.
When you get stuck
Every puzzle on this site can be finished with the techniques above. If nothing seems to move:
- Go back over the lines you have already touched: one new X can turn an old line with too much slack into one that gives way.
- Look at runs that touch an X or the wall (Step 4) — they are easy to miss.
- Check each line whose clue is already complete and cross out the rest (Step 5).
- Press Check in the game. A wrong cell somewhere makes every later deduction unreliable, and it is better to find it early.
- Working on a puzzle from a book or another app? Type its clues into our nonogram solver and step through it one line at a time.
A practice path
Start with 10×10 nonograms and use only overlap and crossing out. Move to 15×15 when you can finish one without pressing Check, then 20×20, where edges and reach start to matter. The daily nonogram is a good habit: one puzzle a day, the same one for everyone.
