debugging skill

---
name: Debugging
description: Systematic debugging framework ensuring root cause investigation before fixes. Includes four-phase debugging process, backward call stack tracing, multi-layer validation, and verification protocols. Use when encountering bugs, test failures, unexpected behavior, performance issues, or before claiming work complete. Prevents random fixes, masks over symptoms, and false completion claims.
version: 3.0.0
languages: all
---

# Debugging

Comprehensive debugging framework combining systematic investigation, root cause tracing, defense-in-depth validation, and verification protocols.

## Core Principle

**NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST**

Random fixes waste time and create new bugs. Find the root cause, fix at source, validate at every layer, verify before claiming success.

## When to Use

**Always use for:** Test failures, bugs, unexpected behavior, performance issues, build failures, integration problems, before claiming work complete

**Especially when:** Under time pressure, "quick fix" seems obvious, tried multiple fixes, don't fully understand issue, about to claim success

## The Four Techniques

### 1. Systematic Debugging (`references/systematic-debugging.md`)

Four-phase framework ensuring proper investigation:
- Phase 1: Root Cause Investigation (read errors, reproduce, check changes, gather evidence)
- Phase 2: Pattern Analysis (find working examples, compare, identify differences)
- Phase 3: Hypothesis and Testing (form theory, test minimally, verify)
- Phase 4: Implementation (create test, fix once, verify)

**Key rule:** Complete each phase before proceeding. No fixes without Phase 1.

**Load when:** Any bug/issue requiring investigation and fix

### 2. Root Cause Tracing (`references/root-cause-tracing.md`)

Trace bugs backward through call stack to find original trigger.

**Technique:** When error appears deep in execution, trace backward level-by-level until finding source where invalid data originated. Fix at source, not at symptom.

**Includes:** `scripts/find-polluter.sh` for bisecting test pollution

**Load when:** Error deep in call stack, unclear where invalid data originated

### 3. Defense-in-Depth (`references/defense-in-depth.md`)

Validate at every layer data passes through. Make bugs impossible.

**Four layers:** Entry validation → Business logic → Environment guards → Debug instrumentation

**Load when:** After finding root cause, need to add comprehensive validation

### 4. Verification (`references/verification.md`)

Run verification commands and confirm output before claiming success.

**Iron law:** NO COMPLETION CLAIMS WITHOUT FRESH VERIFICATION EVIDENCE

Run the command. Read the output. Then claim the result.

**Load when:** About to claim work complete, fixed, or passing

## Quick Reference

```
Bug → systematic-debugging.md (Phase 1-4)
  Error deep in stack? → root-cause-tracing.md (trace backward)
  Found root cause? → defense-in-depth.md (add layers)
  About to claim success? → verification.md (verify first)
```

## Red Flags

Stop and follow process if thinking:
- "Quick fix for now, investigate later"
- "Just try changing X and see if it works"
- "It's probably X, let me fix that"
- "Should work now" / "Seems fixed"
- "Tests pass, we're done"

**All mean:** Return to systematic process.