be in the know

be in the know

slang To be well-informed, especially about a topic that is not widely known. Paige is in the know, so if she says that's the best restaurant in town, we definitely have to go there. Ask Carrie who's going to get the promotion—she's on the executive board, so she's in the know about a lot of things.
See also: know
Farlex Dictionary of Idioms.

be in the know

COMMON If you are in the know about something, especially something that is not known about or understood by many people, you have information about it. These deaths especially affected poor women, since the better off had their babies at home. Those in the know tried to keep out of hospital. Anyone in the know about what had really taken place would have realised immediately that this was dangerous.
See also: know
Collins COBUILD Idioms Dictionary, 3rd ed.

be in the know

be aware of something known only to a few people.
See also: know
Farlex Partner Idioms Dictionary
See also:
  • keep on top
  • dead horse
  • IANA
  • talking head
  • meat and drink to (one)
  • meat and drink to one
  • meat and drink to someone
  • IANAE
  • air (one's) opinion
  • (one) could go (on) all day (about something)