Hashi Puzzles

Common questions

How do you play Hashi?

Hashi, also called Bridges or Hashiwokakero, is played on a grid of numbered islands. Join the islands with straight horizontal or vertical bridges so that each island has as many bridges as its number. A bridge runs only between two islands that see each other along a row or column with open water between them, two islands share at most two bridges, and bridges never cross each other or pass over an island. When you finish, every island must be connected into one group. An island numbered 3 can take a single bridge one way and a double bridge another, since 1 + 2 = 3. Matching every number is not enough if the islands form two separate groups: the board flags a group that is closed off, and the puzzle is not solved until everything joins.

Can I choose the board size?

Yes. Boards come in every size from 5 × 5 to 12 × 12, with about one island for every four to six cells. The same size and seed always build the same puzzle, and Generate from seed accepts any whole-number seed from 0 to 4294967295. New puzzle picks a random seed and skips puzzles already opened in this browser. Challenge scores use the 7 × 7 size; every other size is practice.

Does every puzzle have exactly one solution?

Yes. For each seed the generator grows a connected set of islands from one random island, laying straight single or double bridges to new islands that never touch another island along an edge, then adds some extra bridges where they cross nothing; each island's number is its bridge count. A fast link-by-link search screens the candidate, and then a separate solver that works island by island, without knowing the intended answer, must prove exactly one solution within 100,000 steps before the puzzle is offered. The page repeats that proof when the puzzle opens. A candidate with too few islands or two solutions is discarded, and a proof that reaches its step limit offers nothing; each seed may try up to 64 candidates within 1,000,000 steps. If a seed fails, Generate from seed keeps the previous puzzle and New puzzle moves on to another seed. Steps are counted, not timed, so the same seed builds the same puzzle on every device.

How do hints, undo and reveal work?

Hint corrects one link from the solution: if a link has more bridges than the answer, it lowers that link first; otherwise it adds the missing bridges to one link. Links at the selected island come first, and any hint turns the run into assisted practice. Reveal solution shows the answer while keeping your own bridges underneath. Undo and redo step through your bridge changes until the puzzle is solved; once every rule holds the result is final, and Replay as practice starts the same puzzle again.

How is the Hashi challenge scored?

The challenge is one seeded original 7 × 7 puzzle. Score is 1000 minus your extra placements, never below 0, and higher is better. A placement is each bridge you add: a new single bridge is one placement, and making it double is another. Lowering or clearing a bridge adds none, and a bridge refused because it would cross another adds nothing. Undo takes back the placements it undoes and redo counts them again, until the puzzle is solved. Extra placements are your final retained placements minus the bridges the puzzle needs, which is half the sum of its island numbers, so 1000 is the best possible score. Hint, Reveal solution, an answer key printed before finishing, restored progress, replays and puzzles already opened in this browser, including rotated or reflected copies, stay practice. A scored result stays on the page until you earn a newer one, even when you replay the puzzle or start another. Scores are self-reported.

What happens when someone opens a challenge link?

The page shows the shared score, the fixed rules and a Start same challenge button; nothing starts on its own. The link carries only the seed, the board size setting and the claimed score, never bridges or the answer, and the board is regenerated from the seed at 7 × 7. The button starts one attempt per visit, and a puzzle already opened in this browser stays practice. A link with a fractional, out-of-range, duplicated or wrong-tool value is refused with a message, and ordinary practice opens instead. After a fresh unassisted solve you see both scores, the signed difference and whether you did better, tied or scored lower, with Copy challenge link, Share challenge and Download result card for a new link that carries your score for the same puzzle.

Can I print a puzzle or come back to it later?

Print puzzle prints the numbered islands only, without your bridges or the solution. Print puzzle and answer key adds the answer on a separate page and, if you have not finished, turns the run into assisted practice. The printable copy leaves the page once the print dialog closes. Your board size and seed are saved in this browser, and once you make a change the puzzle's progress is saved too, without the solution. On your next visit an unfinished puzzle reopens automatically, unless you arrive through a challenge link: it is regenerated from its seed and your history is replayed onto it, as practice. Every puzzle that opens or is printed is remembered straight away, up to 1,024 of them, so reloading never turns a puzzle you have already seen into a fresh attempt. Saves keep up to 10,000 changes. If this browser blocks saving, the puzzle stays playable in the open tab, but nothing is remembered after you leave, including which puzzles you opened.

Can I play with a keyboard or on a phone?

Yes. Use the arrow keys to move between islands, Enter or Space to select an island or to build toward the selected one, Shift with an arrow to cycle the bridge in that direction, and Escape to clear the selection. The Bridge from island list, the Up, Right, Down and Left buttons, and Cycle bridge, Remove bridge and Clear selection give the same control without precise tapping. Every island is at least 44 pixels across, and on narrow screens so is every button. Each island's accessible name gives its number, position and bridge count, and the page lists every island's count and state, plus a text version of the board with every placed bridge.