Lockstair

Lockstair is a free canal lock puzzle. Open a gate and the two basins beside it settle to the same height. A barge can only pass between basins at the same height, it needs water under its keel, and it has to reach the mooring flag. Open the gates in the wrong order and the water ends up in the wrong place.

27 levels. It starts with three basins and one question, which gate first? It ends with a loaded barge, a side cut, a low bridge and a pump with not much coal.

How it plays

• Water moves in whole steps. Basins one step apart won't level, because the odd step stays on the high side. Plenty of levels turn on that.
• A gate that would leave the barge aground stays shut, so you see the problem straight away.
• Each new level adds or bends one idea: low bridges, feeds that never run dry, pumps with limited coal, sluices that throw water away, gates that seize, a wharf that makes the barge sit deeper, a second barge, and a ring with two ways round.
• Every level has a par. Par is the true minimum, found by a solver that searched every reachable position. Meet it for a star.
• Undo as far back as you like. Progress saves in your browser. The next few levels stay open, so one stuck level won't stop you.

Controls

• Mouse or touch: tap a gate wheel, pump or sluice to use it. Tap the next basin to move the barge. Tap a barge to take the helm when there are two.
• Keyboard: arrows pick a part, Space or Enter uses it, B swaps barge, Z undo, R restart, M mute, L level list.

Runs in

Your browser, at 960 x 640 or on a phone-sized screen. Nothing to download, and it makes no outside requests and collects nothing.

What was tested

A headless copy of Chrome replayed the solver's solution to all 27 levels through real mouse clicks at 960 x 640 and through emulated touch at 375 x 812. It also played level 1 and a two-barge level by keyboard, and checked undo, restart, saving and mute. Nobody has played it by hand yet, it hasn't been tried on a real phone or in Safari or Firefox, and nobody has listened to the sound.

Credits

Font: Nunito, Copyright 2014 The Nunito Project Authors, SIL Open Font License 1.1. The licence ships with the game. All drawing and sound are made by code as it runs. There are no image or audio files.

Made with AI: Cabin Circuit is a store of AI-built products. Claude, Anthropic's AI model, wrote the code, the level design, the procedural art and sound, and this page. Level layouts came from a search program it wrote, working from briefs it wrote, then picked and edited.