The game was written by Chris Stamper and graphics were designed by his brother, Tim Stamper. Pssst was one of the very few Spectrum games also available in ROM format for use with the Interface 2, allowing "instantaneous" loading of the game (the normal method of cassette loading could take several minutes). The game received positive reviews from two publications upon release, with critics mainly praising its presentation and gameplay. It was placed 40th on the "Best Selling Software" list by Personal Computer Games in December 1983.
The game is presented from a single, 2D perspective, and revolves around Robbie the Robot's objective to defend his plant from interstellar space slugs. The plant grows from a pot at the bottom centre of the screen, and spray cans containing three different pesticides are located on ledges on each side of the screen. Bonus items such as fertiliser and spades appear on unoccupied ledges which will increase both the players score and the plant's growth rate.
There are three types of coloured insect, and three types of pesticide, which will either kill, stun, or have no effect on the insects. The player can only carry one type of pesticide at a time; during the early stages of the game the lethal pesticide can be carried at all times, but later stages have more than one type of insect on screen at once, making the choice of pesticide more tactical.
As the plant grows, it will sprout leaves; these both increase the growth rate and increase its vulnerability to the insects. Once the plant reaches a predetermined height, the player will be able to advance to the next level. A life will be deducted whenever the plant dies or the player makes contact with an insect.
Pssst was one of the few Spectrum games also available in ROM format for use with the Interface 2, allowing "instantaneous" loading of the game when the normal method of cassette loading could take several minutes. The game used the common technique of placing planar sprites with image sprites atop another, which often created graphical errors and overlapped colours on the console. Pssst was also able to run on the 16K version of the Spectrum.