swear by

1. Also, swear to . Have reliable knowledge of, be sure of, as in I think she was going to the library but I can't swear to it . [Mid-1700s]

2. Take an oath by, as in I swear by all the saints in heaven . [Early 1200s]

3. Have great reliance on or confidence in, as in She swears by her personal physician . [Early 1800s]

Example Sentences

Many athletes swear by it, including Michael Phelps and Olympic gymnast Alex Naddour.

From Salon

For those people, many on Reddit swear by the “gray rock” method.

From Slate

There are posters who swear by headbands,highlights, lowlights or stripping — processes that replace your current color with your natural one by matching the shade of your roots or removing dye.

From New York Times

Many influencers, athletes, and regular folks swear by ketogenic diets—skimping on carbs and feasting on fats to quickly shed pounds and improve their metabolism.

From Science Magazine

“I also swear by hardwood floors with inexpensive area rugs versus wall-to-wall carpet with animals. Then, you can wash or replace the area rugs as needed and keep everything clean.”

From Seattle Times