The Mah-Jongg Key is a tile-matching game that uses astrological symbols and multicolored layered tiles instead of ivory tiles that display traditional Mahjong imagery. The goal of the game remains the same. The player must remove all tiles from the playfield to win. They perform this task by matching uncovered tiles with at least one open left or right side. If they run out of matches, they lose.
The game offers blue, black, gold and white tiles as standard sets. The layered pattern also features red and green tiles. The player doesn't need to match the patterns on these tiles to remove them from the field. They merely need to pair any red tile with another red tile and any green tile with another green tile. Lastly, the blue tiles feature the phases of the moon. The player doesn't need to match the quarter phases exactly. They can pair any quarter, no matter the direction.
The Mah-Jongg Key displays the elapsed time, total number of tiles, and total available matches with hint and reset buttons in a framed, semi-transparent square area near the upper-left corner. This frame makes the game more challenging by overlapping some tiles. The player must guess the tiles underneath the non-transparent framed areas.