The player uses an eight-way joystick to move Jack. Two buttons are available to allow Jack to jump or throw beans at enemies. The cycle of screens includes:
Scaling the beanstalk. The player may use his supply of beans to hit and destroy an enemy for points. Jack may also jump from one branch to another, either to gain a new path or avoid an enemy. The player is given a supply of beans to start, and may replenish or add to his arsenal by moving Jack over the beans that appear along the way. Going into the house in this stage will kill Jack.
Walking across clouds to reach the castle's drawbridge, dodging lions and other enemies that try to throw Jack off the tightrope course. The player may enter the castle only when the drawbridge is lowered.
The Giant's lair, which includes ascending stairs to reach the table where the giant's treasures are kept; the giant is seen sleeping at the table. The most frequent danger is navigating the gaps between staircases, dodging flying magic lamps but collecting eggs laid by the golden goose. In the more difficult levels, cats and mice will also appear, which the player must avoid or hit with beans to collect points, and the staircases are narrower. Again, avoiding the enemies, jumping over them or using the magic beans are Jack's defenses.
Descending the beanstalk. In addition to facing the critters in the previous beanstalk stage, Jack must also avoid falling rocks.
The treasures to be stolen include a musical harp, a golden goose, a bag of gold coins and the princess. The player's objective is to retrieve these items on successive trips up the beanstalk, with the princess stage being the last in the four-stage level. A brief animated intermission featuring that specific treasure will play after the player successfully reaches the ground to end each stage. After taking the princess, the giant will awaken, and it is up to the player to descend the beanstalk and chop it down before the giant reaches the ground. Completing a level results in a bonus and the player getting to repeat the cycle at increased difficulty.
Development
Cinematronics president Fred Fukumoto purchased 5,000 game boards from Hara Industries for 2 million US dollars, to be used for Jack the Giantkiller. The hardware came without documentation and had to be reverse engineered.
