code-showcase-systematic-debugging

Systematic Debugging

When to Use

Use this skill when you need four-phase debugging methodology with root cause analysis. Use when investigating bugs, fixing test failures, or troubleshooting unexpected behavior. Emphasizes NO FIXES WITHOUT ROOT CAUSE FIRST.

Core Principle

NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST.

Never apply symptom-focused patches that mask underlying problems. Understand WHY something fails before attempting to fix it.

The Four-Phase Framework

Phase 1: Root Cause Investigation

Before touching any code:

1. Read error messages thoroughly - Every word matters
2. Reproduce the issue consistently - If you can't reproduce it, you can't verify a fix
3. Examine recent changes - What changed before this started failing?
4. Gather diagnostic evidence - Logs, stack traces, state dumps
5. Trace data flow - Follow the call chain to find where bad values originate

Root Cause Tracing Technique:

1. Observe the symptom - Where does the error manifest?
2. Find immediate cause - Which code directly produces the error?
3. Ask "What called this?" - Map the call chain upward
4. Keep tracing up - Follow invalid data backward through the stack
5. Find original trigger - Where did the problem actually start?

Key principle: Never fix problems solely where errors appear—always trace to the original trigger.