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Use Case Builder

Design and implement Python use case functions with dependency injection and type hints.

1|Updated Jul 10, 2025
Search Tags:#software design#python#clean architecture#dependency injection#use case#SOLID principles#application logic
One-click install
npx skills add https://github.com/jzallen/fred_simulations --skill use-case-builder
Or copy as Structured Prompt for Agent▼
Please help me install this Agent Skill.
Skill: Use Case Builder
Source: https://github.com/jzallen/fred_simulations/tree/main/.claude/skills/use-case-builder
Command: npx skills add https://github.com/jzallen/fred_simulations --skill use-case-builder

SYSTEM DOCUMENTATION & REQUIREMENTS

What problem does it solve?

This Skill helps developers design and implement application logic (use cases) that are clean, maintainable, and adhere to architectural best practices like clean architecture and SOLID principles. It prevents spaghetti code and ensures clear separation of concerns, leading to more robust and scalable applications.

Core Features & Use Cases

  • Pure Use Case Functions: Design single-purpose functions for application operations with clear responsibilities.
  • Clear Contracts: Define explicit inputs, outputs, and type hints for robust and predictable use cases.
  • Separation of Concerns: Keep application logic distinct from infrastructure and data access layers.
  • Use Case: Automatically generate a Python use case function for a new feature, ensuring it follows clean architecture, uses dependency injection for repositories, and includes proper type hints and docstrings.

Quick Start

Design a Python use case function named create_new_user that takes a UserRepository and UserData model, validates the data, and returns the created User model.

Frequently Asked Questions about Use Case Builder

High-intent search queries and answers about installing and using this skill.

FAQPage Schema
How do I structure application logic following clean architecture principles?▼

Clean architecture structures application logic into separate layers: domain models, repositories for data access, and use cases that orchestrate operations. Use cases implement single responsibilities, apply dependency injection for repositories, include explicit type hints, and maintain clear separation between business logic and infrastructure concerns.

What's the best way to implement testable Python functions for create, update, and delete operations?▼

Design use case functions with explicit input/output contracts, type hints, and dependency injection for repositories and services. Keep functions stateless, define clear error handling, establish transactional boundaries, and avoid mixing infrastructure logic with business rules. This pattern enables isolated unit testing without external dependencies.

How do I apply SOLID principles and dependency injection to Python application logic?▼

Dependency injection passes repositories and services as function parameters rather than instantiating them internally, enabling flexible mocking and testing. Follow single responsibility by designing each use case function for one operation. Use type hints to enforce contracts and maintain clear separation between application, domain, and infrastructure layers.

Can I prevent spaghetti code in my Python application by enforcing separation of concerns?▼

Yes. Use case functions enforce separation by keeping application logic distinct from data access (repositories) and infrastructure concerns. Each use case handles one operation with a single responsibility, explicit contracts, and dependency injection. This structure prevents tangled dependencies and makes code maintainable as complexity grows.

What should a well-designed use case function include for models, repositories, and controllers?▼

A use case function should accept repositories and services as injected dependencies, define explicit input parameters with type hints, validate domain data, apply business logic, interact with repositories for persistence, include comprehensive error handling with clear failure modes, and return typed output models. Add docstrings explaining behavior and transactional boundaries.

Do I need additional patterns beyond use cases for a complete clean architecture implementation?▼

Use cases form the application layer core, but a complete architecture includes domain models, repositories for data access abstraction, controllers or handlers for entry points, mappers to convert between layers, and services for cross-cutting concerns. Use cases orchestrate these components while maintaining clear contracts and separation between layers.

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