design-an-interface

name	design-an-interface
description	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?

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 1: "Minimise method count - aim for 1-3 methods max"
- Agent 2: "Maximise flexibility - support many use cases"
- Agent 3: "Optimise for the most common case"
- Agent 4: "Take inspiration from [specific paradigm/library]"
- Agent 5 (if the module crosses a Next.js server/client boundary):
  "Design the interface so the server surface is an async function or
   server action, and the client surface is a React hook; justify where
   state lives."

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