Bridges

How to play

Tap or click the space between two islands to build a bridge. Tap again for a second one, and once more to take them both away. Right-click, or press Backspace on a focused pair, to remove one directly.

The number on an island says exactly how many bridge ends touch it. A double bridge counts as two. Bridges run straight across or down, never diagonally, and never cross each other or pass over an island.

The finished network has to connect every island to every other. Two separate groups can satisfy every number perfectly and are still not an answer.

Rules and controls

• A number is an exact count of bridge ends, not a minimum.
• Bridges run horizontally or vertically only.
• At most two bridges join any pair of islands.
• Bridges never cross, and never pass over an island.
• Every island must end up in one single connected network.
• Two islands side by side cannot be joined — a bridge needs a gap to sit in.
• Tab moves between pairs, Enter or Space cycles the focused one, and Backspace removes a bridge.

Modes

• Small 7×7 — The smallest board and the place to start.
• Standard 9×9 — Twenty islands and longer chains of reasoning.
• Large 13×13 — Forty islands and a network that takes a while to close.
• Assisted practice — A bridge that cannot be right is refused. Learn without going wrong.
• Daily Network — One board, the same for everybody, seeded by the UTC date.
• Choose your own — Pick the board and how hard it should be.

Tips

• An island with a high number and few neighbours is nearly forced. A 4 with only two neighbours must send two bridges to each of them.
• A 1 in a corner has one neighbour in each of two directions and uses exactly one of them.
• Once an island has all the bridges it wants, everything else touching it is settled.
• Watch for a group that closes early. If a handful of islands are all satisfied but the rest are not, something in that group is wrong — it can never join the others.
• A bridge you are sure of also rules out everything that would cross it, which is often more useful than the bridge itself.

Privacy and local play

Everything runs in your browser. Your current puzzle, 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

Every island has the right number of bridges but the puzzle will not finish. Why?

Almost certainly because you have two separate networks rather than one. Two groups can satisfy every number perfectly and still not be an answer — every island has to end up connected to every other, and it is the rule people trip over. Look for a group that closed early with the rest left outside it.

Why can I not join those two islands?

If they are next to each other, there is nowhere for a bridge to be — so no bridge between them exists at all, and there is nothing to tap. The same applies when a third island sits between them: the middle one is in the way, so each of the outer two can only reach its nearest neighbour in that direction.

Is a number a minimum or an exact count?

Exact. A 3 means exactly three bridge ends touch that island, never four. A double bridge counts as two ends at each of its islands.

How many bridges can join one pair?

At most two. They are drawn as two separate lines rather than one thick one, so you can always count them at a glance.

How does assisted practice differ?

A bridge that cannot be part of the answer is refused rather than built, so you cannot go wrong at all. That makes it a different game rather than an easier one: instead of trying things and taking them back, you are looking for the next thing that actually follows. It keeps no best times, because a time earned with the route refusing your mistakes is not comparable with one earned without.

What do the difficulty names mean?

A band is measured by solving the board rather than attached to it by the generator. Gentle can be finished purely by working out what each island forces, one step at a time. Steady needs a step or two of looking ahead. Tricky needs more than that: at some point you have to try a bridge and follow it through.

Does the hint ever guess?

No. It only offers a bridge that follows from what is already on the board by the same deductions a player could make, and it says why. When nothing follows in a single step it says so rather than showing a bridge it could not justify. If the board already contradicts itself it tells you that instead of reasoning from a wrong bridge.

Why does Check not tell me which bridges are wrong?

Because that would be a hint wearing a different label, and the route already has one of those. Check tells you how many bridges cannot be right, which is enough to know whether to look again without doing the looking for you.

Can I read the answer out of my browser storage?

No. The board is not stored at all — only which puzzle it was, so it is rebuilt each time — and what is stored beside it is an eight-character hash of the solution rather than the solution. The hash is there so a restored board can be confirmed to be the board that was saved. It is not a security measure and is not offered as one.

Is anything sent to a server?

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

Related interactives

• Slitherlink — one closed loop, with the same connectivity trap.
• Arithmetic Cages — a Latin square with arithmetic targets.
• Kakuro — cross sums, the other arithmetic grid on the site.
• Nonogram — picture logic, also with exactly one solution per board.