show hand

To make one's plans, intentions, ideas, or resources known to others, especially those that were previously hidden or kept secret. (Also expressed as "show (one's) cards"; both phrases refer to displaying one's cards ("hand") during a card game.) In business negotiations, it's important that you don't show your hand right away, or you might risk losing out on the best deal possible. Pressure from the government is forcing the notoriously secretive CEO to show his hand regarding his company's tax profile and offshore accounts.

Fig. to reveal one's intentions to someone. (From card games.) I don't know whether Jim is intending to marry Jane or not. He's not one to show his hand. If you want to get a raise, don't show the boss your hand too soon.

To reveal one’s true motives or intentions. This term, like laying one’s cards on the table, comes from card-playing. Edmund Campion used a version of it in 1581: “I would I might be suffered to shewe my cardes” (Conferences Held in the Tower of London with Ed. Campion, Jesuit, cited by OED). A variant is to tip one’s hand, of the same provenance. The Economist used it on November 17, 1979: “Mr Hunt will not tip his hand on the price at which he will buy more bullion.”