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)

• 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)

• 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)

• 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)

• 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 – Don’t Repeat Yourself principle
• 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: 1.0.0 Status: Active Coverage: 23 rules across 3 categories (SOLID, Core Principles, Design Patterns) Last Updated: 2026-01-17

Rule Statistics

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

License

MIT License

Copyright (c) 2026 Agent Skills

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.