RKCB1430 is used to explore slam, when a trump suit has been agreed 1.
4NT asks how many “key cards”2 do you hold?

1 if the trump suit is not reasonably clear, RKCB is off and ‘normal’ Blackwood (‘ace ask’) applies.
2 A key card is an ace in any suit and the king in the trump suit.


Responses to 4NT

Response Key Cards
5♣ 1 or 4
5♦ 0 or 3
5♥ 2 or 5, no queen of trumps
5♠ 2 or 5, plus queen of trumps


Queen Ask after 5♣/5♦ response

Bid the cheapest non-trump suit

Response to Queen Ask Meaning
Trump Suit no trump queen
5NT trump queen, no side kings
Any non-trump suit trump queen plus king of bid suit

1♣-2♠-4NT-5♣-5♦-5♥ (agrees spades, shows 1/4 KCs, Q♠ and K♥)


Void-showing responses

Instead of the 5 suit level responses, responder can force to slam and show a void + odd/even number of Key Cards

Response Key Cards Void (bid suit not trumps) Void (bid suit trumps)
5NT even (2 or 4) somewhere n/a
6♣ odd clubs any other suit
6♦ odd diamonds hearts or spades
6♥ odd hearts spades

1♣-2♠-4NT-6♥ (agrees ♠, shows odd KCs, void ♥.)


Asking for Kings (5NT)

Normal Blackwood. Note you may have already shown 1 king (via a key card). You show the total number of kings you have. You do not subtract one for the king you may have already declared.


RKCB In Competition

opponent bid after 4NT Action
Double Ignore (or pass)
Suit (eg 5♣) System Off


Why 1430?

Creates more space for the queen at times when it is most useful (and less available when less useful)
…4♥-4NT-5♣ (typically 1 ace and still room for 5♦ queen ask, which is good because slam realistic)
…4♥-4NT-5♦ (typically 0 ace and no room for a queen ask, which is ok because slam no longer realistic)
the other way round with 0314, the queen ask is lost when it is most needed and available when it is less useful.

bridgebum reference