Nonogram (Picross)

Why play here

• No sign-up, no install — quiet, immediate, and good for settling into.
• Unique solutions — only boards with exactly one answer are served, so guessing is never required.
• Pick your size — from small grids up to large ones as you improve.
• Fill and cross — mark cells you have ruled out with an X and the board stops confusing you.
• Times kept — your best is stored on your own device.

How to play a nonogram

The numbers beside each row and above each column tell you how many cells in that line are filled, in consecutive runs. Several numbers mean several runs, in that order, with at least one empty cell between them.

If a line of five cells is labelled "5", the whole line is filled — that is where to start. Work from the lines that are most constrained, cross out what is impossible, and let each certainty narrow its neighbours. Nothing here needs luck.

Nonograms also go by picross, griddlers, paint by numbers, or pixel puzzles. In the Mallow app this game is called Pixel Logic.

Overlap — the move that opens an empty row

There is a way to produce certain cells in a row you know nothing about. It is called overlap, and it works whenever a clue is large relative to the row.

Take a row of 10 cells with a single clue of 8. Push that block of eight as far left as it goes, then as far right as it goes. The middle 6 cells are filled in both arrangements, so they are certain right now. The arithmetic is simply (clue × 2) − row length; whenever that comes out above zero, the technique applies.

Rows with several clues work the same way. Sketch the leftmost possible packing and the rightmost possible packing, then keep only the cells that are filled in both.

Count the slack before you touch a row

A row clued 3 2 4 needs 3+2+4 plus one gap between each block — 11 cells minimum. If the row is 12 long, the slack is a single cell and almost everything is forced. If the slack is generous, that row has nothing to give you yet.

So work in order of slack: tightest rows first, which usually means the rows with the largest clue sum or the most clues. Each cell you settle there tightens the crossing columns, and the chain starts.

X marks are the real tool

• Cap a finished block immediately. Once a block of 3 is complete, the cells on either side must be empty. Mark them, or you will re-derive the same thing next time you read the row.
• Spent clue means the rest is empty. If every filled cell a row calls for is placed, all remaining cells in it are blank — no reasoning needed.
• An X splits a row. One empty cell in the middle divides the row into two shorter segments. Re-measure each, and clues that no longer fit are eliminated — which often reveals an overlap that was invisible a moment ago.

Every board is verified to have exactly one solution, so being stuck never means it is time to guess. It means a row you have not re-read since your last mark still has something in it. Start with the rows crossing the cell you just filled.

Frequently asked questions

Is it really free?

Yes. Every game is free and no account is needed.

Will I have to guess?

No. Every board is generated to have a single logical solution, so it can always be finished by deduction.

Are there other logic puzzles?

Yes — Sudoku, water sort, daily Queens and Tango puzzles, and more than thirty brain games.