~Asking for Keycards

There are five keycards when you use a system that asks for keycards. The keycards are the four aces and the King of trumps. The most common system of Roman Key Card (RKC) is called 1430. The name comes from the meaning of the two lowest responses; i.e., over 4NT, the cheapest response is 5C which shows 1-4 keycards; the next bid up-the-line is 5D and shows 3 or 0 keycards. Put these two together and you get 1430. 

Over 4NT, responses have these meanings:
Bid              RKC (1430)
5C               1 or 4 keycards
5D               0 or 3 keycards
5H               2 or 5 keycards w/o the trump Q
5S                2 or 5 keycards with the trump Q

You can readily see that RKC provides more useful information than does Blackwood. Once keycards are shown, 5NT asks for kings and promises that the partnership holds all the keycards. Responses are
6C: 0 or 4 kings
6D: 1 king
6H: 2 kings
6S: 3 kings

NOTE: Many top players play “Specific Kings.” In this system, over 5NT, responder bids the cheapest K.

If playing RKC, do not show the trump K twice. If you showed that K as a keycard, do not show it as a king also.

If hearts are trumps and the bidder wants to play 5NT as a final contract, once keycards are shown below the 5S level, bidder may bid 5S to tell partner to bid 5NT.

Example:
You             Partner
1H              3H
4NT            5H
5S               5NT
P
You believe that 5NT is the best contract but cannot bid 5NT without partner showing kings. You can get to 5NT by bidding 5S (an impossible contract in this bidding sequence), asking partner to bid 5NT.