Clean Code Principles

Fundamental software design principles, SOLID, design patterns, and clean code practices. Language-agnostic guidelines for writing maintainable, scalable software.

When to Apply

Reference these guidelines when:

• Designing new features or systems
• Reviewing code architecture
• Refactoring existing code
• Discussing design decisions
• Improving code quality

Rule Categories by Priority

Quick Reference

1. SOLID Principles (CRITICAL)

• solid-srp - Single Responsibility Principle
• solid-ocp - Open/Closed Principle
• solid-lsp - Liskov Substitution Principle
• solid-isp - Interface Segregation Principle
• solid-dip - Dependency Inversion Principle

2. Core Principles (CRITICAL)

• core-dry - Don't Repeat Yourself
• core-kiss - Keep It Simple, Stupid
• core-yagni - You Aren't Gonna Need It
• core-separation-of-concerns - Separate different responsibilities
• core-composition-over-inheritance - Favor composition
• core-law-of-demeter - Principle of least knowledge
• core-fail-fast - Detect and report errors early
• core-encapsulation - Hide implementation details

3. Design Patterns (HIGH)

• pattern-factory - Factory pattern for object creation
• pattern-strategy - Strategy pattern for algorithms
• pattern-repository - Repository pattern for data access
• pattern-decorator - Decorator pattern for behavior extension
• pattern-observer - Observer pattern for event handling
• pattern-adapter - Adapter pattern for interface conversion
• pattern-facade - Facade pattern for simplified interfaces
• pattern-dependency-injection - DI for loose coupling

4. Code Organization (HIGH) — planned

• org-feature-folders - Organize by feature, not layer
• org-module-boundaries - Clear module boundaries
• org-layered-architecture - Proper layer separation
• org-package-cohesion - Related code together
• org-circular-dependencies - Avoid circular imports

5. Naming & Readability (MEDIUM) — planned

• name-meaningful - Use intention-revealing names
• name-consistent - Consistent naming conventions
• name-searchable - Avoid magic numbers/strings
• name-avoid-encodings - No Hungarian notation
• name-domain-language - Use domain terminology

6. Functions & Methods (MEDIUM) — planned

• func-small - Keep functions small
• func-single-purpose - Do one thing
• func-few-arguments - Limit parameters
• func-no-side-effects - Minimize side effects
• func-command-query - Separate commands and queries

7. Comments & Documentation (LOW) — planned

• doc-self-documenting - Code should explain itself
• doc-why-not-what - Explain why, not what
• doc-avoid-noise - No redundant comments
• doc-api-docs - Document public APIs

Essential Guidelines

For detailed examples and explanations, see the rule files:

• [core-dry.md](rules/core-dry.md) - Don't Repeat Yourself principle
• [pattern-repository.md](rules/pattern-repository.md) - Repository pattern for data access

SOLID Principles (Summary)

Core Principles (Summary)

Quick Examples

// Single Responsibility - one class, one job
class UserService {
  constructor(
    private validator: UserValidator,
    private repository: UserRepository,
  ) {}

  createUser(data) {
    this.validator.validate(data);
    return this.repository.create(data);
  }
}

// Dependency Inversion - depend on abstractions
interface Repository<T> {
  find(id: string): Promise<T | null>;
  save(entity: T): Promise<T>;
}

class OrderService {
  constructor(private repository: Repository<Order>) {}
}

// DRY - single source of truth
const EMAIL_REGEX = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
const isValidEmail = (email: string) => EMAIL_REGEX.test(email);

// Meaningful names over magic numbers
const MINIMUM_AGE = 18;
if (user.age >= MINIMUM_AGE) { }

Output Format

When auditing code, output findings in this format:

file:line - [principle] Description of issue

Example:

src/services/UserService.ts:15 - [solid-srp] Class handles validation, persistence, and notifications
src/utils/helpers.ts:42 - [core-dry] Email validation duplicated from validators/email.ts
src/models/Order.ts:28 - [name-meaningful] Variable 'x' should describe its purpose

How to Use

Read individual rule files for detailed explanations:

rules/solid-srp-class.md
rules/core-dry.md
rules/pattern-repository.md

References

This skill is built on established software engineering principles:

Core Books

• Clean Code by Robert C. Martin - Foundation for clean code practices
• Design Patterns by Gang of Four - Classic design pattern catalog
• Refactoring by Martin Fowler - Improving code structure
• The Pragmatic Programmer by Hunt & Thomas - Practical wisdom

Online Resources

• Refactoring Guru - Design patterns and code smells
• Martin Fowler's Refactoring Catalog - Comprehensive refactoring techniques
• Uncle Bob's Clean Coder Blog - Software craftsmanship articles

Pattern Catalogs

• Refactoring Guru - Design Patterns
• Martin Fowler - Enterprise Patterns

Metadata

Version: 1.0.2 Status: Active Coverage: 23 rules across 3 implemented categories (SOLID, Core Principles, Design Patterns); 4 planned Last Updated: 2026-03-07

Rule Statistics

• SOLID Principles: 10 rules
• Core Principles: 12 rules
• Design Patterns: 1 rule