hold (one's) cards close to (one's) chest

hold (one's) cards close to (one's) chest

To keep one's plans, intentions, or information secret from everyone else. Refers to holding one's playing cards close to one's chest in a game, so as not to allow other players to see one's hand. We're all curious about what the boss has been discussing in those meetings with the lawyers, but she's been holding her cards close to her chest. Sorry for not being more straightforward about my plans, but I'm holding my cards close to my chest for the time being.
See also: card, chest, close, hold
Farlex Dictionary of Idioms.

keep/hold/play your cards ˌclose to your ˈchest

not tell others what you are intending to do: He keeps his cards pretty close to his chest. I don’t know whether he plans to buy the house or not. OPPOSITE: show/reveal your hand
See also: card, chest, close, hold, keep, play
Farlex Partner Idioms Dictionary
See also:
  • (from) top to toe
  • be on (one's) pat
  • at (one's) doorstep
  • at doorstep
  • at expense
  • at somebody's expense
  • at someone's expense
  • at (one's) expense
  • be in (one's) good graces
  • be in somebody's good graces