In JARS, the narrative is told mainly through wordless cutscenes and comic strips to strong effect. Without spelling anything out, the game introduces the main character, Victor, and shows that since babyhood, he's helped his mad scientist father in the lab -- until a recent experiment unleashed something sinister. Now, Victor is on a quest through various areas in his family's basement to uncover secrets. Each level of the game, which features a tower defense mechanic, is a step further along the path. In the levels, the player uses minions (small creatures experimented on by Victor's father) to protect wooden sarcophagi (or coffins) from nasties like rats, spiders, and slugs. The sarcophagi are located on shelves, which the nasties and minions traverse via ladders. In gameplay, the player smashes jars that are located on the shelves to reveal either minions, tools, or nasties. Some jars are clearly marked as either bad or good, but most are unmarked. The player's job is to smash jars, collect minions and tools, and use them to defeat the nasties before the sarcophagi are breached. Beyond placing minions and using tools wisely, players can also find success by selecting power-ups for the minions before the level starts, most of which can be purchased from the in-game store using currency earned with each completed level. Other features and systems are introduced throughout the game, but they only arrive once players have sufficiently mastered the basics. There's also an alternative option to the story mode called 'hero mode' in which the player controls a small hero that crosses the shelves and not only smashes jars but fights nasties itself. Hero mode gives players the option to earn significant in-game currency, but only if they leave their run at a high point. If they fail a level, in-game currency is deducted and they must start again at a beginner level.