As an opening Edit
- 1♦ opening in five-card major systems typically shows a four-card or better suit. Rarely (only with 4=4=3=2 shape) is it only three cards. Typically with 4-4 minors, one opens 1♦.
- In four-card major systems, a 1♦ opening promises 4 ♦s.
- In a strong club system, 1♦ is usually the catch-all opening for all opening hands that don't have another opening bid available.
- In a strong diamond system, 1♦ is the strong, artificial and forcing opening, typically promises 16+ HCPs and nothing about the shape.
As a response Edit
- A 1♦ response to a natural 1♣ opening promises at least 4 ♦s.
- In a strong club system, a 1♦ response to a strong 1♣ opening is negative, about 0-7 HCPs.
As an overcall Edit
- A 1♦ overcall normally promises 5+ good ♦s (occationally 4 very good ♦s) and about 8-16 HCPs.