What is Hashiwokakero?

Hashiwokakero (橋をかけろ, “build bridges!”) is a Japanese logic puzzle published by Nikoli, also known as Bridges, Hashi or Ai-Ki-Ai. A grid of numbered islands has to be joined by bridges: every island gets exactly as many bridges as its number, bridges run straight and never cross, at most two join the same pair of islands, and in the end every island can be reached from every other. Like Sudoku or Nurikabe it needs no arithmetic, only deduction.

How to play Bridges online

Pick a difficulty from Easy (7×7) to Oni (24×24) and press Generate. Click the water between two islands to build a bridge, click again for a double bridge, a third click removes them, or simply drag from one island to the next. Finished islands turn green, overfull ones red. Stuck? Ask for a hint, or let the solver check your bridges. The full rules with a solved example are on the how to play page.

Solving techniques that avoid guessing

• An island whose number equals twice its neighbours has a double bridge to every one of them: an 8 in the open, a 6 on an edge, a 4 in a corner.
• A 1 never connects to another 1, and two 2s are never joined by a double bridge, that would cut them off from the rest.
• Count what is still missing: if an island needs 5 more bridges across three neighbours, each neighbour gets at least one.
• Bridges block the lines they cross, so a placed bridge can force the islands on both sides to connect elsewhere.
• Everything has to end up connected: a group that can only reach the rest through one gap must use it.

Why play Hashi here

• Every puzzle has exactly one solution, proven by a SAT solver before you see it, so logic alone is always enough.
• Unlimited free puzzles in five sizes, with hints and checks that come from the real solution, not from heuristics.
• Cute Japanese pixel art, a day and a night theme, keyboard shortcuts, undo and redo, and your game is saved in the browser.
• Make your own puzzles in the workshop, or watch our own CDCL and DPLL SAT solvers race in the lab. The whole game is open source and written in Rust.