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Use when investigating bugs, errors, or unexpected behavior. Activates when something is broken and needs diagnosis. Enforces root-cause analysis before any fix attempt.
Codex または Claude でインストール この Prompt をコピーして Codex、Claude、または他のアシスタントに貼り付けると、Skill ページを確認してインストールできます。
SOC 職業分類に基づく
Create Excalidraw diagram JSON files that make visual arguments. Use when the user wants to visualize workflows, architectures, or concepts.
Create Mermaid diagrams in markdown. Use when the user wants to visualize workflows, architectures, API flows, data models, state machines, or system designs. Covers flowcharts, sequence diagrams, class diagrams, ER diagrams, state diagrams, and more.
React Hook Form best practices, validation with Zod, performance patterns, and testing. Use when building, reviewing, or refactoring forms, form validation, useForm, useFieldArray, Controller, or integrating React Hook Form with UI libraries.
Web application security best practices based on OWASP Top 10:2025. Use when reviewing code for vulnerabilities, implementing auth/authorization, handling user input, working with file uploads, managing secrets, or building API endpoints. Covers React, Express, MongoDB, and JWT security.
Use when writing, reviewing, or planning tests for Express controllers, routes, middleware, validators, and Mongoose models in server/. Covers Vitest, Supertest, mongodb-memory-server, auth testing, and project-specific conventions.
General-purpose React Testing Library guide with Vitest. Use when writing, reviewing, or setting up React component and hook tests. Covers project setup from scratch, RTL query priority, userEvent, async patterns, mocking strategies, and common anti-patterns. Applicable to any Vite + React project.
| name | systematic-debugging |
| description | Use when investigating bugs, errors, or unexpected behavior. Activates when something is broken and needs diagnosis. Enforces root-cause analysis before any fix attempt. |
A structured approach to finding and fixing bugs. No guessing, no random changes.
No fixes without root cause first. If you can't explain WHY the bug happens, you don't understand it well enough to fix it.
Tip: For bugs that need runtime instrumentation (race conditions, timing issues, memory leaks), also consider Cursor's Debug Mode (
Cmd+.→ Debug). This skill defines the reasoning process; Debug Mode provides the runtime tooling.
Before forming any hypothesis, collect facts:
git log --oneline -10
git diff HEAD~1
npm run db:logs)Look for patterns in the evidence:
| Pattern | Likely Cause |
|---|---|
| Works locally, fails in production | Environment variable or build config issue |
| Works on first load, fails on navigation | Client-side routing or state issue |
| Intermittent failures | Race condition, timing, or network issue |
| Works for some data, fails for others | Data validation or edge case |
| Error after dependency update | Breaking API change in dependency |
| 401/403 on API calls | JWT token expired or missing auth middleware |
| CORS errors | Server CORS config doesn't match client origin |
| MongoDB connection errors | Docker not running or connection string wrong |
Based on evidence, form a specific hypothesis:
Template: "The bug occurs because [specific cause] which results in [observed behavior] when [trigger condition]."
In your commit message or PR description, include:
Stop and reassess:
In these cases: simplify, add logging, and gather more evidence.