[mike777]

Coming back to bridge after many years I have been watching a lot of BBO bridge before I embarrass myself at the table.

I have noticed this basic auction create issues among all levels of players.

1C-(1S)-X


What are the expected minimum types of hands for this negative double?

[jdiana]

At least 7-8 HCP, usually four hearts.

[jillybean]

 jdiana, on 2024-November-18, 14:38, said:

At least 7-8 HCP, usually four hearts.

6-9

[jdiana]

 jillybean, on 2024-November-18, 14:41, said:

6-9

I don't think it's limited, actually. 2♥ would show 10+ points and five hearts. With only four hearts, I would start with a negative double. But I think people have differing agreements about this double. As usual, the answer is "whatever you and your partner agree."

[DavidKok]

The minimum hands in double contain 4(+) hearts. It is possible partner is strong with exactly 4♥, but not possible that partner is strong with 5(+)♥ as partner would bid 2♥ with that hand type. In theory there is no upper limit to the number of hearts, but in practice doubling with 6(+) tends to fare poorly.

Lastly double may also be a 'smallest lie' with 3 hearts, but this is uncommon, typically stronger, and more of an intermediate+ agreement.

[mycroft]

Yes, standard is "4 or more hearts, enough to bid at the two level; but not '5 hearts and 10 HCP'." Agreements can vary from standard in many ways (not least how strong is "enough to bid at the 2 level").

[mike777]

Follow up question
1C=(1S)=X=P
2D=P=2H?

What hand is responder representing?

[DavidKok]

6-9 with (5)6+ hearts.
More importantly, you should discuss which hand opener is representing. Some people insist that double implies diamond tolerance or extra hearts, so that 2♦ is weak. More common is to let go of that requirement for the double, with the consequence that the 2♦ rebid requires significant extra strength.