foolproof

/ˈfuːlpruːf/

fool·proof

BrE /ˈfuːlpruːf/

NAmE /ˈfuːlpruːf/

(of a plan, machine, method, etc.)

very well designed and easy to use so that it cannot fail and you cannot use it wrongly

SYN infallible

This recipe is foolproof—it works every time.