Design Expert

This is your reference implementation for system design patterns and distributed systems concepts. It covers the fundamentals you'd expect in a senior engineering interview: CAP theorem, circuit breakers, rate limiting, caching strategies, database sharding, and load balancing algorithms. The code examples are clean and practical, like the circuit breaker with three states and the cache-aside pattern implementation. What I appreciate here is it's not just theory. You get working Python implementations of patterns you can actually adapt, from singleton and factory to write-through caching and weighted round-robin load balancing. It's basically a cheat sheet for building scalable systems, with enough depth to be useful but not so much you're drowning in academic theory.

skills.sh installs: 176
GitHub stars: 44
last updated: Aug 21, 2026

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Install

$ npx -y skills add personamanagmentlayer/pcl --skill design-expert --agent claude-code

Installs into .claude/skills of the current project.

Files

System Design Expert

Expert guidance for system design, software architecture, scalability patterns, and distributed systems.

Core Concepts

Architecture Patterns

Microservices vs Monolithic
Event-driven architecture
CQRS and Event Sourcing
Layered architecture
Hexagonal architecture
Service-oriented architecture (SOA)

Scalability

Horizontal vs vertical scaling
Load balancing strategies
Caching layers
Database sharding
Read replicas
CDN usage

Distributed Systems

CAP theorem
Consistency models
Distributed consensus (Raft, Paxos)
Message queues
Service discovery
Circuit breakers

Design Patterns

# Singleton Pattern
class DatabaseConnection:
    _instance = None
    _lock = threading.Lock()

    def __new__(cls):
        if cls._instance is None:
            with cls._lock:
                if cls._instance is None:
                    cls._instance = super().__new__(cls)
                    cls._instance._initialize()
        return cls._instance

    def _initialize(self):
        self.connection = self._create_connection()

SKILL.md on GitHub