Abbreviation of You Ain’t Gonna Need It. YAGNI is a principle of XP that sets that a programmer should not add functionality until deemed necessary. code example

Example: YAGNNI

"You aren't gonna need it" is a principle of extreme programming that states a programmer should not add functionality until deemed necessary. XP co-founder Ron Jeffries has written: "Always implement things when you actually need them, never when you just foresee that you need them."