Numberlink / Flow Puzzle

What is a Numberlink puzzle?

Numberlink, often sold as Flow, is a path-connection puzzle played on a square grid. The grid is dotted with pairs of matching numbers — two 1s, two 2s, two 3s and so on. Your task is to draw a single continuous path between each pair of matching numbers. The catch is that the paths are not allowed to cross or overlap, and in the classic version every square in the grid must be used by exactly one path. The result is a satisfying tangle of routes that snake around one another to fill the board completely.

Because there is one tidy solution and the rules are easy to state, Numberlink is a brilliant warm-up for spatial reasoning. It rewards planning ahead rather than guesswork, and it works just as well for a quick five-minute break as it does for a quiet classroom starter. Every puzzle this tool produces is built from a complete, valid solution first, so the endpoints you see on the page can always be joined up exactly as intended.

The rules in full

• One path per pair. Each numbered endpoint must connect to the other cell carrying the same number with a single unbroken line.
• Move through edges only. Paths travel up, down, left and right between neighbouring squares — never diagonally.
• No crossing or sharing. Two paths may not pass through the same square, and a path may not cross over itself.
• Fill the board. In the standard puzzle every square ends up covered by exactly one path, leaving no empty cells.

That last rule is what gives Numberlink its tight, no-loose-ends feel. If you find squares left over, a route somewhere needs to take a longer detour.

How to solve it

Start with the endpoints tucked into corners and along the edges. A number sitting in a corner has only two ways out, so its path almost decides itself for the first few steps. Trace those forced moves first and you will quickly carve up the easy regions of the board. Next, look for narrow channels — a single line of empty squares pinched between two finished paths must belong to whichever pair can legally reach it.

A useful habit is to keep checking the fill rule as you go. If completing one path would seal off a square so that no other route can ever reach it, that path is wrong and must take a wider sweep. Strong solvers think of the grid as a budget: every square must be spent exactly once, so a path that hugs the wall too tightly often starves a neighbour. Pencil lightly, and do not be afraid to send a path the long way around — elegant solutions are frequently the curviest ones.

Choosing size and difficulty

The grid size sets the overall challenge: a 5x5 board is gentle and quick, while 8x8 and 9x9 grids demand real forward planning. The difficulty setting changes how many numbered pairs appear. Fewer pairs mean longer, sweeping paths that are easier to route; more pairs break the board into shorter, interlocking journeys that are trickier to fit together without crossing. Pick a smaller grid with the easy setting for younger children, and a larger grid on hard for puzzle fans who want a proper workout.

Using the printable

Set your grid size and difficulty, then watch the live preview update. Press Generate New for a fresh layout, or type a seed to reproduce the exact same puzzle later — handy when you want the whole class working on identical boards. Toggle the answer key on to add a second page where every pair is joined by a colour-coded path, so marking takes seconds. Add the Name and Date fields for classroom sets. Everything prints cleanly on A4 or US Letter through the same branded template as the rest of the site.