# Solid Principles

> Use when: apply SOLID principles to make object-oriented code flexible and maintainable.

- Skill: `kimtth/solid-principles` (Agent Skill)
- Install (CLI): `npx skillmds@latest add kimtth/solid-principles`
- Raw SKILL.md: https://api.skillmd.com/api/skills/kimtth/solid-principles/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: kimtth (https://skillmd.com/u/kimtth)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/kimtth/solid-principles

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Goal: code whose responsibilities and dependencies are clear and stable.

Use for:
- reviewing class responsibilities and coupling
- guiding a refactor toward maintainable structure
- explaining why a design is hard to change

Workflow:
1. Single responsibility: one reason to change per unit.
2. Open/closed: extend behavior without modifying stable code.
3. Liskov: subtypes must honor the base type's contract.
4. Interface segregation: small interfaces over fat ones.
5. Dependency inversion: depend on abstractions, not details.
6. Apply only where it removes real pain.

Smells the principles address:
- god classes and shotgun surgery (SRP)
- modifying core code for every new case (OCP)
- subclasses that break expectations (LSP)
- clients forced to depend on unused methods (ISP)
- high-level code chained to low-level details (DIP)

Rules:
- principles are guidance, not dogma; avoid over-abstraction
- prefer the simplest design that stays changeable
- introduce abstraction at the second real use, not the first
- a clear, cohesive unit beats a clever hierarchy