20×20 nonograms

Twenty squares a side is a proper session: a detailed picture that rewards a plan. Pick a difficulty and start.

What changes at 20×20

With 400 squares you can no longer hold the whole board in your head. The long clues are where the certainty is, so plan from the longest clues and let them seed the short lines around them.

On a phone, pinch to zoom: the board keeps its five-square guides at every zoom level, so you never lose count.

Techniques that matter. The five techniques are the same ones you already know. What changes is how many lines you have to juggle: forty of them, twenty rows and twenty columns. Keep a rhythm of sweeping the rows, then the columns, and only then go hunting for a clever move. A line with a long run and a lot of slack can wait; it usually becomes easy once its neighbours are crossed.

Tips for 20×20

1. Rank lines by total. Add each clue's runs and gaps; the lines closest to 20 are where to start.
2. Work in bands of five. Finish what you can between two guides before moving on.
3. Zoom for precision, zoom out to plan. Fill at a size you can tap accurately, then step back to pick the next line.

Expert boards can't be finished with line-by-line reasoning alone. You'll need lookahead (see How to play).