design

name	design
description	Architecture and design consultation for applications. Use this skill when discussing system architecture, design patterns, tech stack decisions, API design, or module structure. Covers Unix/Linux Philosophy for CLI tools and Twelve-Factor App for web applications and microservices.

Design Consultation

Use this skill when discussing architecture, design patterns, or system structure.

Workflow

1. Identify the application type and the matching design philosophy:
   • CLI tools, scripts, system utilities → Unix/Linux Philosophy
   • Web applications, APIs, microservices → The Twelve-Factor App
   • Libraries, shared modules → both (Unix for API design, Twelve-Factor for deployment)
2. Apply the checklist for the identified type. Raise concerns where the current design violates principles.
3. Provide recommendations with rationale. When trade-offs exist, explain the pros/cons and recommend the simpler option.

Unix/Linux Philosophy Checklist

• Single responsibility per module/function ("do one thing well")
• Composable via standard I/O — stdout for output, stderr for diagnostics
• Meaningful exit codes (0=success, non-zero=error); fail fast with clear messages
• Explicit over implicit behavior; safe defaults, flags required for dangerous operations
• No hidden side effects

Twelve-Factor App Checklist

• No hardcoded config — store config in environment variables
• Dependencies explicitly declared in a manifest (package.json, go.mod, etc.)
• Stateless processes (no local session state); scale out via the process model
• Logs to stdout as event streams (no local log files)
• Fast startup and graceful shutdown; health check endpoints
• Dev/prod parity; admin tasks as one-off processes