paulund/plan-design-interface

Design an Interface

Based on "Design It Twice": your first idea is unlikely to be the best. Generate radically different designs in parallel, then compare.

Workflow

1. Generate Designs (Parallel Sub-Agents)

Spawn 3+ sub-agents simultaneously. Each must produce a radically different approach.

Design an interface for: [module description]

Requirements: [gathered from user]

Constraint for this design: [assign a different constraint to each agent]
- Agent 1: "Minimize method count - aim for 1-3 methods max"
- Agent 2: "Maximize flexibility - support many use cases"
- Agent 3: "Optimize for the most common case"
- Agent 4: "Take inspiration from [specific paradigm/library]"

Output format:
1. Interface signature (types/methods)
2. Usage example (how caller uses it)
3. What this design hides internally
4. Trade-offs of this approach

2. Compare

After showing all designs, compare on:

• Interface simplicity: fewer methods, simpler params
• General-purpose vs specialized: flexibility vs focus
• Implementation efficiency: does shape allow efficient internals?
• Depth: small interface hiding significant complexity (good) vs large interface with thin implementation (bad)
• Ease of correct use vs ease of misuse

Discuss trade-offs in prose, not tables. Highlight where designs diverge most.

3. Synthesize

Ask: "Which design best fits your primary use case? Any elements from other designs worth incorporating?"

Anti-Patterns

• Don't let sub-agents produce similar designs — enforce radical difference
• Don't skip comparison — the value is in contrast
• Don't implement — this is purely about interface shape
• Don't evaluate based on implementation effort