Nonogram technique 6 of 12

Glue: a box near the edge pins the first clue

A box close to the border has only one run it can belong to. That run is stuck to it, and some of its neighbours are stuck too.

Clue 5 in ten squares with a box on square 3. The run of 5 covers squares 1 to 5 at the furthest left and 3 to 7 at the furthest right; squares 3 to 5 are shared.

In our words

Why a box near the edge is pinned

Take a row of ten with the single clue 5 and a box on square 3. The run of five must cover square 3. Slide it as far left as it goes and it covers 1 to 5. Slide it as far right as it can while still covering square 3 and it covers 3 to 7. Squares 3, 4 and 5 are in both positions, so they are boxes. The glue is square 3 holding the block against the edge.

The condition is simple: the box must be no farther from the border than the length of the first clue. If it is farther than that, the box might belong to the second clue and nothing is certain.

Practice: a 6x6 grid that needs glue

The edge boxes of this grid cannot be reached by plain overlap. Look for a box one or two squares from a border.

Tap a square to fill it. Not sure where to begin? Press "Show the step".

How we checked this grid: our solver knows nine named rules. With all of them it solves the grid in 21 line moves. With glue switched off it stops with 15 of 36 squares known. The first move that uses glue comes at step 2.

Your marks are saved in this browser, so you can come back to the grid.

In our words

The mirror and the moving wall

Everything works from the other end too, with the last clue. And a crossed-out square can act as a wall. If the first three squares are crossed, treat square 4 as the border, then apply the same rule.

The special case people learn first is a box on the very first square. The first clue starts right there, so you can fill the whole run and, by punctuating, cross out the square after it.

The move in three steps

Find the first box. Look at the first box from the edge, ignoring crossed squares.
Check the distance. Is it closer to the border than the first clue is long?
Fill the shared squares. Fill from that box to the end of the run when pushed against the border.

Worked example: both ends

A row of twelve has the single clue 5 and a box on square 3. On its own that clue has seven squares of slack and fills nothing. But the run has to include square 3. Pushed to the start it covers squares 1 to 5, and the furthest down it can sit while still touching square 3 is squares 3 to 7. Squares 3, 4 and 5 are in both, so they are boxes.

From the far end it works the same way. A line of ten with the clue 2 3 and a box on square 9 pins the last run: it reaches square 7 at the least and square 10 at the most, so squares 8 and 9 are boxes too.

Common slip. Gluing a box to the first clue when the box is farther from the edge than that clue is long. It could be the second run.

Glue, as Wikipedia describes it

Each link opens the source at the exact sentence.

Sometimes, there is a box near the border that is not farther from the border than the length of the first clue. sourceWikipedia: Nonogram
In this case, the first clue will spread through that box and will be forced outward from the border. sourceWikipedia: Nonogram
In the simplest case, whenever a box is present in the first or last cells of a row or column, the first or last clue must be aligned to the edge of that row or column. sourceWikipedia: Nonogram
It is therefore possible to mark the third, fourth and fifth cell as belonging to the 5. sourceWikipedia: Nonogram

Sources: Wikipedia, Nonogram (revision 1377687149, read 2026-11-01). Wikipedia text available under CC BY-SA 4.0, edited by Wikipedia contributors. The source link after each sentence goes to the passage it comes from.