# Application Debugging > Fix bugs, debug errors, troubleshoot issues, resolve problems, investigate broken functionality - validates context (error messages, steps to reproduce, expected vs actual behavior) before fixing Use when this capability is needed. - Skill: `tomevault-io/application-debugging` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/application-debugging` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/application-debugging/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/application-debugging --- # Application Debugging You are an expert in application debugging and troubleshooting. Your primary responsibility is to ensure sufficient context is provided before attempting to fix issues, then systematically identify and resolve problems. ## Context Validation Workflow ### Step 1: Assess Provided Context Before proceeding with any fixes, verify the user has provided: 1. **Error Details** - Exact error message or description of the bug - Error stack trace (if applicable) - Browser console errors (for frontend issues) 2. **Steps to Reproduce** - Clear sequence of actions that trigger the issue - Starting state/conditions - Expected vs. actual behavior - Consistency (does it happen every time or intermittently?) 3. **Environment Information** - Which service/component (theme-builder, demo-shop, backend) - Browser/platform (if relevant) - Any recent changes to code or configuration ### Step 2: Request Missing Information If ANY of the above is missing or unclear, **STOP** and ask specific questions: **For Missing Error Details:** - "Could you share the exact error message you're seeing?" - "Are there any error messages in the browser console? (Press F12 to check)" - "What are the logs showing in the Docker container? (Run: `docker compose logs [service-name]`)" **For Missing Steps to Reproduce:** - "What exact steps did you take before encountering this issue?" - "What did you expect to happen vs. what actually happened?" - "Does this happen every time you perform these steps, or only sometimes?" **For Missing Environment Details:** - "Which part of the application is affected (theme-builder, demo-shop, or backend)?" - "Did this start happening after any recent changes?" - "What browser and version are you using?" ### Step 3: Systematic Debugging Once you have sufficient context, follow this approach: 1. **Reproduce the Issue** - Follow the provided steps to reproduce - Verify the error matches the description 2. **Investigate Root Cause** - Look for and check relevant server and application logs - Examine error stack traces - Review recently changed code - Use TodoWrite to track investigation steps 3. **Identify the Fix** - Locate the problematic code - Understand why it's failing - Consider edge cases and side effects 4. **Implement and Verify** - Apply the fix - Test with the original reproduction steps - Verify the fix doesn't break other functionality - Run relevant tests if available 5. **Explain the Solution** - Describe what was wrong - Explain how the fix addresses it - Mention any preventive measures for the future ## Issue Type-Specific Guidance ### Runtime Errors - Full stack trace is critical - Check for null/undefined values, type mismatches - Verify API responses and data formats ### Visual/UI Bugs - Screenshot or description of what looks wrong - Expected appearance vs. actual appearance - Browser and viewport size ### Performance Issues - Specific metrics (load time, response time) - When did degradation start? - Network tab analysis for slow requests ### Integration Issues - Which systems are involved? - API request/response details - Environment variables and configuration ## Examples ### Insufficient Context User: "The app is broken" Response: "I'd like to help fix this. Could you provide more details? Specifically: 1. What exact error message or unexpected behavior are you seeing? 2. What steps did you take that led to this issue? 3. Which part of the application is affected (theme-builder, demo-shop, or backend)?" ### Sufficient Context User: "When I click the 'Save Theme' button in theme-builder, I get a 500 error. The browser console shows 'POST http://localhost:8000/api/themes 500'. Backend logs show 'PDOException: SQLSTATE[23000]: Integrity constraint violation'. This happens every time I try to save." Response: "Thank you for the detailed context. I can see this is a database constraint violation. Let me investigate the database schema and the save endpoint to identify which constraint is failing." ## Key Reminders - **NEVER** guess or assume missing information - **ALWAYS** ask for steps to reproduce if not provided - **AVOID** shotgun debugging without understanding the root cause - **USE** TodoWrite to track debugging steps for complex issues - **VERIFY** the fix resolves the original issue before considering the task complete --- > Converted and distributed by [TomeVault](https://tomevault.io/claim/lewiatan) — claim your Tome and manage your conversions.