Guide
How to solve a nonogram
Every puzzle on this site can be solved by reasoning alone. You never need to guess. Here is the whole method, one technique at a time.
How the clues work
The numbers beside a row or above a column list the runs of filled squares in that line, in order. A clue of 3 1 means a run of three, then at least one blank, then a single filled square. The numbers never tell you where the runs start — only their sizes and their order.
Full lines and exact fits
Start with any line where the clues plus their mandatory gaps exactly fill the width. A clue of 5 in a five-wide row fills the entire row. A clue of 2 1 in a four-wide row can only be filled, filled, blank, filled. These are free squares — take them all before doing anything harder.
Overlap
When a run is longer than half its line, some squares are filled no matter where the run sits. Slide the run as far left as it goes, then as far right. Any square covered both times must be filled. A run of four in a five-wide row overlaps on the middle three squares.
Marking empty squares
Marking a square you know is empty is as valuable as filling one. Empty squares cut lines into shorter segments, and short segments are where exact fits appear. If a segment is smaller than the smallest remaining run, the whole segment is empty.
Edge logic
A filled square touching the edge of a line anchors the run next to it. If the first clue is 2 and the first square is filled, the second square must be filled too, and the third must be empty.
When you get stuck
Switch axes. A row that gives nothing often becomes obvious after two columns are resolved. If nothing at all moves, re-check a line you thought was finished — on this site a genuine dead end means a mistake, never a puzzle that needs a guess.