Roman Key Card Blackwood (Key Card, RKC, 0314, 1430) is a variation of the slam convention Blackwood. It counts the king of the agreed trump suit as an 'ace', thus enabling pairs to check for aces and the king of trumps when probing for slam. The responses to 4NT RKC are:

5: Shows 0 or 3 key cards
5: Shows 1 or 4 key cards
5: Shows 2 key cards without the trump queen
5: Shows 2 key cards with the trump queen

The 4NT bidder can usually tell whether responder has 0 or 3 key cards after a 5 response, and 1 or 4 key cards after a 5 response. As for responder holding all five key cards - in practice it never occurs. Responder always seems to hold at least one of the five key cards in order to be looking for slam.

The 1430 variations of Roman Key Card Blackwood swaps the meanings of the 5 and 5 responses; using 1430, 5 shows 1 or 4 key cards and 5D shows 0 or 3.

After a conventional response, the 4NT bidder can then bid 5NT, asking partner to bid his cheapest (non-trump) king.

There are a number of ways to show key cards if 4NT is overcalled. One way is called DOPI, which stands for "Double = 0 (or 3) key cards, Pass = 1 (or 4)." The cheapest available bid shows two key cards, the second-cheapest bid shows three key cards, and the third-cheapest bid shows four. Another method of showing key cards is DEPO, which stands for "Double = Even number of key cards, Pass = Odd number of key cards."

Note that on occasion the responder to an RKC inquiry will have a void somewhere in his hand. Voids should not be treated as key cards; how they are treated instead is up to partnership agreement.

Finally, it is important to agree with partner when RKC is on, and when it is off. Sometimes one player wants to just ask his partner how many real aces he holds, and this can cause a lot of confusion at a fatally high bidding level. Entire books have been written on RKC, so handle the convention with care.