Writing Use Cases

Documents

writing-use-cases

Writing Use Cases is an Agent Skill for documents published in the majiayu000/claude-skill-registry repository on GitHub: a SKILL.md instruction file an AI agent can load to do this task.

Create structured use case documentation with sequence diagrams for backend systems. Use when documenting API endpoints, service interactions, event flows, or system behaviors. Triggers on requests like "document this use case", "create use case for X endpoint", "write flow documentation", or "explain how X feature works".

View on GitHub ↗

QUICK START

How to use this skill

Bring this guide into your coding agent with a prompt tailored to the tool you use.

Open your project in Codex.
Copy and paste the prompt below.
Review files and risks before approving any action.

Prompt to paste

Inspect the Agent Skill at https://github.com/majiayu000/claude-skill-registry/blob/HEAD/skills/data/writing-use-cases/SKILL.md and all supporting files. Report provenance, permissions, scripts, dependencies, and security risks. Propose an exact installation into .agents/skills/writing-use-cases, but wait for my approval before writing files or running scripts.

Copying this prompt does not install or run the skill. Review third-party files before use.

Writing Use Cases

Create use case markdown files that document backend flows with mermaid sequence diagrams.

Discovery Workflow

Identify entry point - Find the controller/handler for the endpoint
Trace the flow - Follow method calls, service interactions, external calls
Find events - Look for message publishing (SNS, Kafka, RabbitMQ, etc.)
Map state transitions - Identify entity state changes
Note validations - Document validation rules and constraints

Output Structure

# {Feature Name} Use Case

## Overview
{1-2 sentences: what this use case does and when it's triggered}

## Flow

{mermaid sequence diagram - see references/mermaid-patterns.md}

## Key Points

- **Entry Point:** `{HTTP method} {path}` ([`{ControllerName}`]({relative-path}))
- **Request Model:** [`{DtoName}`]({relative-path})
- **State Transition:** {from} → {to}
- **Event:** `{EventName}` published to {destination}
- **Validation:** {key validation rules}

Output File

Use the docs/{use case name}-use-case.md as output file location (DEFAULT).
Ask the User, if the default is fine or another location should be used.

Writing Guidelines

Keep overview concise (1-2 sentences)
Use relative links to source files
Include all actors and systems in the diagram
Group related operations with Note over blocks
Use alt/else for conditional flows
Document both success and error paths when relevant

Mermaid Patterns

See references/mermaid-patterns.md for sequence diagram syntax and examples.