Meaning of “swear by sth” - Learner’s Dictionary

swear by sth

phrasal verb with swear uk us /sweər/ verb (past tense swore, past participle sworn)

to believe strongly that something is useful or effective:

Have you tried using vinegar to clean windows? My Mum swears by it.

(Definition of “swear by sth” from the Cambridge Learner’s Dictionary © Cambridge University Press)