Nonogram by Big T

The numbers beside each row and column are the runs of filled squares, in order.

A clue of 3 1 means a run of three, then at least one empty square, then a run of one. The gaps can be any length — working out where the runs sit is the puzzle.

Mark the squares you know are filled, and cross out the ones you know are empty.

Crossing out is not just bookkeeping. Every X narrows where the remaining runs can go, and most deductions come from squares you've ruled out.

The puzzle is done when every filled square matches its row and column clues.

The two buttons above the board decide what a tap does — fill a square, or cross it out.

The active mode is highlighted. Switching is quicker than it looks, and an X you place now is information you'll use later.

Crosses out the leftovers in a row or column as soon as its clues are satisfied.

Saves the tidying-up once a line is finished. The button under the board shows the current state, and the Auto-Mark switch in Settings does the same thing.

Steps back one mark at a time.

Clears the board and starts the same puzzle again from scratch.

A run longer than half its line always fills some cells, wherever it sits.

In a 10-cell row with a single clue of 8, slide the run as far left as it goes, then as far right. Cells covered both times must be filled — here that is six of them, and you have not decided anything about where the run actually starts. The bigger the clue relative to the line, the more it gives you. This is why the largest clues are the right place to begin.

A filled cell near an edge pins the run that contains it.

If the first clue in a row is 4 and the second cell is already filled, the run cannot start later than cell 2, so cells 2 through 4 are filled whatever else is true. Edges constrain harder than the middle because a run has nowhere to slide.

An X is not bookkeeping — it is the thing that makes the next deduction possible.

Every X splits a line into shorter segments, and short segments cannot hold long runs. A segment of three cells cannot contain a clue of 4, so that clue must live elsewhere, which often forces it precisely. Players who only fill squares stall constantly; the crossing-out is where the information is.

When a line's clues are all placed, every remaining cell in it is empty.

Turn Auto X on and the app does this for you the moment a line completes. Doing it is not optional — those Xs are the segment boundaries the crossing lines need.

Runs need at least one empty cell between them, and that spacing is a constraint.

Clues of 3 2 in a 7-cell line need 3 + 1 + 2 = 6 cells minimum, leaving one cell of slack. With that little freedom, overlap applies to both runs at once. Adding up the clues plus the mandatory gaps and comparing against the line length tells you immediately how much room you are working with.

Every cell you settle in a row is new information for a column, and vice versa.

Nonograms are solved by alternating. If a row will not yield, the reason is usually that you have not yet spent what the columns already know. A puzzle that feels stuck almost always has an available deduction on the other axis.

Every puzzle here is solvable by logic from the clues alone.

If you are reduced to guessing, there is a deduction still on the board — most often an overlap in a long clue or a segment too short to hold the run you are trying to place.

Easy 7×7, Medium 9×9, Hard 12×12, Expert 15×15.

A bigger grid is harder for two compounding reasons: there are more lines to track, and each line is longer, which means the clues constrain a smaller share of it. Overlap does less work on a 15-cell line than on a 7-cell one.

Small grids fall to overlap and edges; large ones need segment reasoning.

On a 7×7 the clues are large relative to the line and much of the puzzle falls straight out of overlap. By 12×12 and 15×15 the early grid is sparse, and progress comes from crossing out, splitting lines into segments, and alternating between rows and columns.

Flags squares that don't match the solution.

Show or hide the solve timer.

Switch between light and dark, and pick a colour theme.