Hash Blocks is a falling-blocks puzzle game similar to Columns. Blocks fall in sets of three from the top of the well, and can be cycled and rotated freely. If four blocks of the same type are lined up horizontally, vertically, or diagonally, they are cleared and removed from the playfield, causing any blocks above them to fall into the open space. If the blocks reach the top of the screen, the game is over.

The game includes two modes. Normal mode tasks the player with clearing a certain number of blocks before the playfield fills up. Flash mode requires the player to clear a specific, flashing block, which may be buried under multiple other blocks. Both modes offer three levels of difficulty, as well as multiple different block graphic sets to use.