Gulper.io is a battle-arena snake game. The player's goal is to direct a black snake with neon spots and accents to gulp glowing, multi-colored energy pellets for as long as possible.
The player attempts to feed their snake to make it grow larger than all the other snakes slithering across the arena. They can feed it small energy pellets that appear randomly. They can also feed it large balls of energy that appear after another snake dies in the arena. Snakes die if they collide with other snakes or the walls. A head-on collision kills both snakes.
Gulper.io requires the player to select a nickname or use a preselected guest name. If the player wants to join a specific private room, they must use their nickname followed by the @ symbol and the name of the room.
The game also features several top leaderboards. The player can track their rank position in an arena by reviewing a vertical list along the top-right side of the screen. On the home screen, they can also look at the daily, monthly and all-time rankings by using the trophy icon.