3.7 KiB
name, description
| name | description |
|---|---|
| design-an-interface | Generate multiple radically different interface designs for a module using parallel sub-agents. Use when user wants to design an API, explore interface options, compare module shapes, or mentions "design it twice". |
Design an Interface
Based on "Design It Twice" from "A Philosophy of Software Design": your first idea is unlikely to be the best. Generate multiple radically different designs, then compare.
Workflow
1. Gather Requirements
Before designing, understand:
- What problem does this module solve?
- Who are the callers? (other modules, external users, tests)
- What are the key operations?
- Any constraints? (performance, compatibility, existing patterns)
- What should be hidden inside vs exposed?
Infer these from the request and existing callers; ask only about missing requirements that materially affect the designs.
2. Generate Designs (Parallel Sub-Agents)
Compare meaningfully different approaches, honoring the requested count. Two is a useful default for "design it twice"; add options only when they explore a relevant trade-off. Use independent subagents through the available delegation tool when useful and within available slots; otherwise develop the alternatives directly.
Prompt template for each sub-agent:
Design an interface for: [module description]
Requirements: [gathered requirements]
Constraints for this design: [assign a different constraint to each agent]
- Option A: "Optimize for the primary caller's workflow"
- Option B: "Expose explicit state transitions for the same requirements"
Choose constraints relevant to the actual problem; do not invent future use cases or a target method count.
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
3. Present Designs
Show each design with:
- Interface signature - types, methods, params
- Usage examples - how callers actually use it in practice
- What it hides - complexity kept internal
Present designs sequentially so user can absorb each approach before comparison.
4. Compare Designs
After showing all designs, compare them 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
Use the requested format or the clearest concise comparison. Highlight where designs diverge most.
5. Synthesize
Recommend the best fit with reasons. If the user wants to choose interactively, ask:
- "Which design best fits your primary use case?"
- "Any elements from other designs worth incorporating?"
Evaluation Criteria
From "A Philosophy of Software Design":
Interface simplicity: Fewer methods, simpler params = easier to learn and use correctly.
Scope fit: Covers known callers and requirements without speculative flexibility.
Implementation efficiency: Does interface shape allow efficient implementation? Or force awkward internals?
Depth: Small interface hiding significant complexity = deep module (good). Large interface with thin implementation = shallow module (avoid).
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
- Include implementation effort and migration risk in the trade-offs without letting them obscure correctness or usability.