keep your cards close to your chest

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

To keep one's plans, intentions, or tactics secret from everyone else. Refers to holding one's playing cards close to one's chest in a card 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 keeping her cards close to her chest. Sorry for not being more straightforward about my plans, but I'm keeping my cards close to my chest for the time being.
See also: card, chest, close, keep
Farlex Dictionary of Idioms.

keep (or play) your cards close to your chest (or vest)

be extremely secretive and cautious about something. informal
The previous two idioms both refer to a hand of cards in a card game. If you hold all the cards you have a winning hand, while card players who hold their cards close to their bodies ensure that no opponent can look at them.
See also: card, chest, close, keep
Farlex Partner Idioms Dictionary

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
References in periodicals archive
Summary: In the high-stakes game of Middle East diplomacy, it's advisable to keep your cards close to your chest.
American paper tiger
Keep your cards close to your chest, Princess.") was not the best route for her after all.
Me and the Blondes
Keep your cards close to your chest if you're taking a late summer break - even if you don't go abroad.
Don't fall for the holiday card trick