Nonogram solver that shows its steps
Type in the row and column numbers of any black and white nonogram (also called picross or griddlers) and this free solver fills the grid, one explained step at a time, or all at once. It runs in your browser, sends nothing anywhere and shows no ads.
Separate the numbers in a clue with spaces. Write 0 for an empty line. The two lists must add up to the same number of filled squares. The sample above is a small 5 by 5 puzzle, so press Solve all to see how it works.
How it solves
For each line the solver lists every way the clue's runs could still fit given what is already known, then keeps only what is true in all of them. If a square is filled in every possible arrangement it is filled, and if it is empty in every one it is empty. It repeats this over rows and columns until nothing changes. That is exactly the line logic a person uses, so every step it prints is one you can check by hand. It never guesses.
What the answers mean. "Solved" means line logic alone completed the grid, so the answer is the only one. "Stuck" means line logic ran out: the puzzle either needs a guess to continue or has more than one answer, and the grid shows what is certain so far. "No solution" means the clues contradict each other, which usually means a typo. Grids up to 25 by 25 are accepted. For the daily picture puzzle that uses the same rules, play Stencil, and to learn the techniques read how to solve nonograms.