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

Priority	Category	Impact	Prefix
1	SOLID Principles	CRITICAL	`solid-`
2	Core Principles	CRITICAL	`core-`
3	Design Patterns	HIGH	`pattern-`
4	Code Organization	HIGH	`org-`
5	Naming & Readability	MEDIUM	`name-`
6	Functions & Methods	MEDIUM	`func-`
7	Comments & Documentation	LOW	`doc-`

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 - Don't Repeat Yourself principle
pattern-repository.md - Repository pattern for data access

SOLID Principles (Summary)

Principle	Definition
Single Responsibility	A class should have only one reason to change
Open/Closed	Open for extension, closed for modification
Liskov Substitution	Subtypes must be substitutable for base types
Interface Segregation	Don't force clients to depend on unused interfaces
Dependency Inversion	Depend on abstractions, not concretions

Core Principles (Summary)

Principle	Definition
DRY	Don't Repeat Yourself - single source of truth
KISS	Keep It Simple - avoid over-engineering
YAGNI	You Aren't Gonna Need It - build only what's needed

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

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

clean-code-principles