Foolproof
/ˈfuːlˌpruːf/
Synonyms
- certain
- infallible
- reliable
- fail-safe
- unfailingly
Slang Meanings
So simple that even a fool can do it.
Programming this app is foolproof; even my grandma could do it.
Guaranteed to succeed without any issues.
This strategy is foolproof – there's no way it can fail.