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?
Ask: "What does this module need to do? Who will use it?"
2. Generate Designs (Parallel Sub-Agents)
Spawn 3+ sub-agents simultaneously using Task tool. Each must produce a
radically different
approach.
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]
- 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
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
Discuss trade-offs in prose, not tables. Highlight where designs diverge most.
5. Synthesize
Often the best design combines insights from multiple options. 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.
General-purpose
Can handle future use cases without changes. But beware over-generalization.
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
Don't evaluate based on implementation effort