Number Link

How to play

Drag from a number to draw its path, with a mouse or a finger. Let go to stop; pick the path up again from its own head. With a keyboard, Tab reaches the board once and the arrow keys move around it — Enter picks a path up, and the arrow keys then draw it.

Every number appears exactly twice. Paths run up, down, left and right, never diagonally, and no two paths may share a square.

In every preset but the minimal-clue challenge, every square must end up on a path — the shaded squares are the ones still to cover.

Rules and controls

• Each number appears twice, and the two must be joined.
• Paths move one square at a time, never diagonally.
• A square belongs to one path. Paths cannot cross or overlap.
• A path cannot branch — it is one line from a number to its twin.
• Drawing through another path cuts that path back to just before the square you took.
• Except in the minimal-clue challenge, every square must end up on a path.
• Undo and redo go a whole stroke at a time — U and R, or the buttons.

Modes

• 6×6 — Eleven pairs on a small grid. The place to start.
• 8×8 — Twenty pairs, and every square has to end up on a path.
• 10×10 — Thirty-three pairs filling a hundred squares.
• Minimal clue — The 8×8 grid with a quarter of its numbers taken away. Join them all; empty squares are fine.
• Daily Link — One board a day, the same for everybody, from the UTC date.

Tips

• Start in the corners. A number in a corner has two ways out at most, and often only one, so those paths are already decided.
• Watch the edges. A path that runs along an edge and strands a single square behind it has gone wrong, because that square can never be covered.
• Two numbers next to each other are usually not joined by the short route. If they were, the squares around them would have nothing to cover them.
• Draw freely. Cutting through another path is a normal move, not a mistake, and undo takes back a whole stroke.
• On the minimal-clue board, think about which squares can only be reached by one path at all. With fewer numbers there is more empty space and fewer forced moves, so the constraints that do exist are worth more.

Privacy and local play

Everything runs in your browser. Your current board, your settings and your best times are kept on this device only, and the button under the board clears them without touching any other Zerdly tool. No account, no sign-in, and nothing about your play leaves the machine you are on.

Questions

How is this different from Path Pairs?

They are the same family of puzzle, and Zerdly builds both because they are genuinely different games to play. Number Link uses bigger boards — 6×6, 8×8 and 10×10 against 5×5, 7×7 and 9×9 — numbers instead of letters, and a minimal-clue challenge that Path Pairs has no equivalent of. Underneath, both use the same rules and the same solver, which is deliberate: one engine with one set of tests is safer than two copies that can drift apart.

What is the minimal-clue challenge?

The 8×8 board with a quarter of its numbers taken away — fifteen pairs instead of twenty. Fewer numbers means longer, more ambiguous paths, and it is measurably harder rather than merely labelled so: a solver needs more than twice the work on the same grid. It is also the one preset where you do not have to cover every square. Joining the pairs is enough.

What happens if I draw through another path?

That path is cut back to just before the square you took, and everything before it stays. The move is not refused. Reusing space is most of the work on a big board, so making you clear the other path first would be several seconds of tidying for every idea you wanted to try. Dragging back along your own path erases it the same way.

I have joined every number. Why does it not say solved?

Because in every preset but the minimal-clue challenge, every square has to end up on a path. A board with all its numbers joined and three empty squares is not finished. The top strip shows how many squares are covered, and the uncovered ones are shaded.

Does every board have exactly one solution?

Yes, and it is proved rather than assumed. A board is built by cutting a single path that already covers every square into pieces, then a solver counts the answers; it is kept only when there is exactly one. If the search runs out of its budget the board is discarded rather than shipped with a guess. Ten thousand generated boards were checked this way before launch.

Why do two pairs have the same colour?

Because there are six colours and a 10×10 board has thirty-three pairs. Colour is only there to help two paths crossing near each other read as two paths — the number is what says which pair a square belongs to. Thirty-three colours a colour-blind player could tell apart do not exist, so nothing on this page depends on colour alone.

Does the hint ever guess?

No. It searches from the position you are actually in and names the next square of one path, so it always fits what you have already drawn. It is worked out fresh each time and can never be advice about a position you have undone. Boards finished with a hint still count as solved, but they do not set a best time.

What do the difficulty names mean?

A band is measured by solving the board rather than attached to it by the generator: it counts the work a full proof of uniqueness costs. The cuts differ by size, because a bigger board takes more work at every level — and the bands on the 6×6 are closer together than on the 10×10, because a small board does not hold enough ambiguity to spread them widely.

How does the daily puzzle work?

One board a day, the same for everybody, built from the UTC date rather than your local one. The board is regenerated from the date rather than stored, which is why the generator version is part of the key. Your results stay on this device.

Is anything sent to a server?

No. The generator, the solver, the hints, the sounds and your progress all run in your browser. There is no account, and clearing this game's data leaves every other Zerdly tool untouched.

Related interactives

• Path Pairs — the same family on smaller boards, with letters and a relaxed preset instead of a minimal-clue one.
• Block Fit — place three shapes at a time and clear whole rows and columns.
• Traffic Escape — sliding pieces on a crowded grid, with a way out to find.
• Slitherlink — draw a single loop that satisfies every clue.