Conventions in depth
Once a trump suit is agreed, 4NT asks for five keycards, the four aces and the trump king, and for the trump queen.
Ordinary Blackwood counts the four aces. Roman Keycard Blackwood (RKCB) also counts the king of trumps, which is as important as an ace once a trump suit is agreed.
BidMaestro plays the 1430 answering scheme (the name is a memory aid for the two cheapest replies).
The one-or-four and zero-or-three pairings are not ambiguous: the rest of the auction tells the asker which of the two it is.
Ten trumps count as the queen. If the partnership is sure of at least ten trumps between them, you can give the “with the queen” reply even without it. With so many trumps the queen rarely matters: when the king is missing, it costs one trick with or without the queen; when an ace is missing, the queen will usually fall under the ace and king.
When the reply was 5♣ or 5♦ (the two replies that have not yet resolved the trump queen), the asker can bid the cheapest non-trump suit to ask for it. Partner then:
With all five keycards and the trump queen accounted for and a grand slam in view, a bid of 5NT asks for kings. Partner shows specific outside kings up the line at the six level (or jumps to the grand with a source of extra tricks). This lets the partnership place a grand slam only when the last kings are known, not guessed.
A useful void is worth telling partner about, so the responses make room for it:
The aim is to stop at the five level when a keycard is missing, and to bid slam only when the count (aces, trump king, and trump queen) is complete. RKCB answers all three questions where old-fashioned Blackwood answered only the first.
Before asking, check that every answer leaves you somewhere you can play. The replies climb, and the trump suit decides how much room there is.
With hearts agreed, the 5♠ reply, two keycards and the queen, is already past 5♥. Hold one keycard yourself and that reply means two are missing, with no way back to five. So asking on a one-keycard hand is dangerous in hearts, where with spades agreed you could always stop at five.
A minor is worse again. The replies run past five of the trump suit almost at once, so the ask commits the partnership to a level its answer may not justify. With a minor agreed, control bids and judgement place the contract better than a count of keycards.
Opponents sometimes bid over 4NT to jam the count. The count carries on. Over their suit bid the partnership plays DOPI, where double takes over as the cheapest reply and the step responses continue in order above their call. If they double 4NT, ROPI works the same way, starting with redouble.
4NT is Roman Keycard Blackwood only once a trump suit has been agreed. In a notrump auction with no agreed suit, 4NT is instead a natural, quantitative raise, and 4♣ Gerber is the tool for asking about aces. BidMaestro keeps these apart automatically.
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