Sandbox

A sand-block puzzle: slide blocks up to sand of their colour and clear the board.

What it does

Each level is a crowded grid with reservoirs of layered, coloured sand. Drag a block next to sand of its colour and the grains pour in; at 100% the block pops. Some blocks hold two colours, inner first. Key blocks open padlocked blocks, and some blocks slide along one row or column only. Clear every block to finish the level.

How it's built

• One HTML file. The sand is a real simulation: grains are pulled out of the reservoir on the block's side, the grains above slump into the hole, and only grains a block can actually reach come to it.
• Every level is generated from its number, with a difficulty curve that shrinks the air on the board, adds keys, two-colour blocks and one-direction blocks as the levels climb.
• A solvability check runs during generation: each block must be able to slide under the whole width of the reservoir that holds its sand, in a solve order the generator chose.
• A headless bot plays every level through the page's own code before a change ships.