“Agility is a measure of your overall finesse and reflexes. It affects the number of Action Points in V.A.T.S. and your ability to sneak.”— in-game description
Agility defines a character's Defense, or their ability to avoid damage. Agility is also added with Perception to determine a character's Initiative. Agility is also used as the default for skill tests involving Small Guns, Sneak, and Throwing.
Agility affects how efficient a dweller is while working in the diner and garden facilities. It can be increased on different dwellers by assigning them to the athletics room.
While on quests, Agility also increases how fast (how many times) a dweller attacks/ fires their weapon per round.
Fallout: The Board Game[]
Unlike other games, Agility is not treated as a variable ranging from 1 to 10, but instead as a token that can be obtained at the start or when leveling up. A player character with the Agility token gets free rerolls during certain tests, as well as during fights if equipped with an Agility-based weapon.
The wastelander player character always begins the game with Agility. Any player character wearing the singed duster gains one hit during an Agility test. However, a player character cannot gain any rerolls from Agility while wearing metal armor. During any Agility test, Calmex can be used to gain one free hit.