Checked with the free nonogram checker at blobsmith.lbwma.com/nonogram-checker · 10 free printable nonograms: blobsmith.lbwma.com/free-nonograms
Draw a picture below. This reads the clues off your drawing and then answers the question a clue generator can't: is there exactly one grid that fits those clues, and can a person reach it with row-and-column logic alone? When the answer is no, the cells logic cannot decide are marked in orange — that is the part of the drawing to change. Nothing you draw leaves your browser.
Click a cell to fill it, drag to paint a run. Every filled square is part of the picture; the clues are counted from it.
Counting the runs in a drawing is the easy half, and every nonogram maker online does it. The half that decides whether anybody enjoys your puzzle is whether those clues lead somewhere: one picture, reachable step by step, without ever stopping to try a cell and see what happens.
Two different things can go wrong, and both come out of this page as the same warning because they have the same cure:
The classic cause is a feature one pixel wide — a lone antenna, a 1px diagonal, a floating dot — with nothing around it to pin it down. Widening it to two pixels usually fixes the puzzle and barely changes the picture.
The button above loads a 15×15 camera we drew for the motif library and never shipped. As drawn, it is clean: one answer, reached in 3 passes of row-and-column logic. Press "Add one pixel" and a single cell changes at row 13, column 15 — the picture is still obviously a camera, and the puzzle is now broken: 4 cells that no amount of row-and-column reasoning can settle. They light up orange. That is the entire difference between a puzzle that a person finishes and one they abandon, and it is invisible to the eye.
This is not a demo we wrote by hand: the build searches the grid in reading order for the first single-cell change that costs the picture its uniqueness, and refuses to publish the page if it can't find one or if the browser copy disagrees about how many cells go undecided.
This isn't a check written for a web page. It is the rule that admits a picture into our books: derive the clues from the art, solve them with logic alone, and require the answer to come back identical to the art — otherwise the drawing gets redrawn, never the clues loosened. Every one of the 106 pictures in our motif library was iterated against it, some for several rounds, which is why so many of them have two-pixel antennae and no 1px diagonals.
The build that produced this page re-ran that verdict over all 110 puzzles we have published — 100 in the book and 10 in the free pack — and got "clean" 110 times out of 110. It also refuses to publish if the copy running in your browser disagrees with ours on a single cell or a single pass.
If you'd rather solve than design, the same engine drives the solver, which works from clues instead of a drawing, and the four deduction rules are explained with drawn examples in how to solve nonograms step by step.
A4 PDF, no sign-up. Every one cleared the check above before the file went out. Download the free pack — or play the same ten in your browser, no pencil needed.
The paid book: 100 puzzles in three sizes, each proved to have a single solution reachable without guessing. See it on itch.io
Letting students design each other's nonograms, and the lesson plan around it: nonograms in the classroom.