solid

Use this skill when writing code, implementing features, refactoring, planning architecture, designing systems, reviewing code, or debugging. This skill transforms junior-level code into senior-engineer quality software through SOLID principles, TDD, clean code practices, and professional software design.

449stars57forksUpdated 6/19/2026

Developer Tools #clean-code #code-quality #software-engineering #solid-principles #tdd #refactoring

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About solid

The Solid skill transforms your code from junior-level implementations into senior-engineer quality software by enforcing professional software engineering practices. It applies SOLID principles, Test-Driven Development (TDD), and clean code practices to every line of code you write. This skill ensures that code is not just functional, but testable, flexible, and maintainable—designed to serve users cost-effectively over the long term.

This skill enforces a rigorous Red-Green-Refactor TDD cycle where tests are written first, followed by the simplest implementation, then refactored for quality. It applies the five SOLID principles (Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, Dependency Inversion) to every class and module. The skill mandates clean code practices including meaningful naming conventions, primitive wrapping with value objects, first-class collections, and adherence to the Law of Demeter. Design decisions happen during refactoring, not during initial coding.

This skill is ideal for software engineers who want to elevate code quality, teams implementing domain-driven design, projects requiring long-term maintainability, and anyone learning professional software craftsmanship. It applies to feature implementation, refactoring, architecture planning, code reviews, debugging, and test creation across any programming language or framework.

FAQ

When should I use the Solid skill?

Use this skill whenever you're writing code, implementing features, refactoring, planning architecture, designing systems, reviewing code, or debugging. It applies to all software development activities where code quality and maintainability matter.

Does this skill work with any programming language?

Yes. While examples in the skill documentation use TypeScript, the SOLID principles, TDD methodology, and clean code practices apply universally to any object-oriented or functional programming language including Python, Java, C#, Go, Rust, and JavaScript.

Do I have to write tests first every time?

Yes. The skill enforces Test-Driven Development as a non-negotiable practice. You must follow the Red-Green-Refactor cycle: write a failing test first, implement the simplest solution to pass it, then refactor. This is one of the core principles of professional software engineering in this skill.

What are value objects and why are they mandatory?

Value objects wrap primitive types (strings, numbers) in domain-specific classes like UserId, Email, or Money. They're mandatory because they enable type safety, encapsulate validation logic, make code self-documenting, and prevent primitive obsession—a common code smell that reduces maintainability.

Is this skill suitable for small scripts or only large applications?

While the skill emphasizes practices most beneficial for maintainable, long-lived codebases, the principles scale down effectively. For throwaway scripts, you may choose not to apply this skill. For any code that will be read, modified, or maintained by others (or future you), these practices provide immediate value.