---

name: applying-code-principles description: > Fundamental software principles - SOLID, DRY, Occam's Razor, Miller's Law, YAGNI. Triggers: 原則, シンプル, 複雑, アーキテクチャ, リファクタリング, 保守性, コード品質, design pattern, best practice, clean code allowed-tools: Read, Grep, Glob user-invocable: false

Code Principles

Claude knows all principles. This file defines project-specific thresholds and priority.

Priority Order

When principles conflict:

1. Safety First - Security, data integrity
2. YAGNI - Don't build what you don't need
3. Occam's Razor - Simplest solution
4. SOLID - For complex systems
5. DRY - Eliminate duplication (not at cost of clarity)
6. Miller's Law - Respect 7±2 cognitive limit

Quick Decision Questions

• "Is there a simpler way?" (Occam's Razor)
• "Understandable in <1 min?" (Miller's Law)
• "Duplicating knowledge?" (DRY)
• "Needed now?" (YAGNI)
• "Single reason to change?" (SOLID/SRP)

Thresholds

Miller's Law

Target	Ideal	Max	Limit
Function args	3	5	7
Class methods	5	7	9
Conditionals	3	5	7

DRY

• Rule of Three: Abstract on 3rd duplication

SOLID

• Create interface only when 2nd implementation appears
• No single-implementation interfaces

YAGNI

Before adding, confirm:

1. Problem exists now? → No = don't build
2. Failed in production? → No = no error handling yet
3. User requested? → No = no feature yet
4. Measured evidence? → No = no optimization yet