Black Box Architecture Skill

This skill teaches Claude to apply Eskil Steenberg's battle-tested black box architecture principles for building modular, maintainable software systems.

Philosophy

"It's faster to write 5 lines of code today than to write 1 line today and then have to edit it in the future." — Eskil Steenberg

Optimize for:

• Human cognitive load over algorithmic efficiency
• Long-term maintainability over short-term cleverness
• Team scalability (one person per module)
• Constant developer velocity regardless of project size

Core Principles

1. Primitive-First Design - Identify core data types that flow through your system
2. Black Box Boundaries - Modules communicate only through documented interfaces
3. Replaceable Components - Any module can be rewritten using only its interface
4. Single Responsibility - One module = one person can own it
5. Wrap Dependencies - Never depend directly on code you don't control

Variants

This skill has three specialized variants that are automatically selected based on your request:

Refactor Variant

When to use: Code refactoring, breaking apart monoliths, creating module boundaries

Triggers:

• "Refactor [code/class/module]"
• "Break apart this monolith"
• "Create black box modules"
• "Analyze [component] and suggest modular refactoring"

File: refactor.md

Plan Variant

When to use: Strategic architecture planning, designing new systems

Triggers:

• "Design architecture for [system]"
• "Plan the module structure"
• "How should I architect [feature]"
• "Design a [type] system"

File: plan.md

Debug Variant

When to use: Systematic debugging, testing strategies, integration issues

Triggers:

• "Debug [issue]"
• "Fix this bug"
• "Why is [component] failing"
• "Test strategy for [feature]"

File: debug.md

Output Format

All variants follow a structured 4-phase protocol and produce consistent output:

## 🔍 Current Architecture
[Primitives, modules, coupling issues, violations]

## 🎯 Proposed Black Box Design
[Module designs with interfaces]

## 📝 Implementation Steps
[Specific, actionable steps]

## ⚠️ Risks & Mitigation
[What could go wrong + how to prevent]

## ✅ Quality Gates
[Validation checklist]

Supported Languages

• Python
• TypeScript/JavaScript
• Go
• Rust
• C
• PHP
• Java

Learn More

Based on Eskil Steenberg's lecture: Architecting LARGE Software Projects