Quick Reference: The Four Phases

Phase	Key Activities	Success Criteria
1. Root Cause	Read errors, reproduce, check changes, gather evidence	Understand WHAT and WHY
2. Pattern	Find working examples, compare	Identify differences
3. Hypothesis	Form theory, test minimally	Confirmed or new hypothesis
4. Implementation	Create test, fix, verify	Bug resolved, tests pass

Red Flags - STOP and Follow Process

If you notice yourself considering:

"Quick fix for now, investigate later"
"Just try changing X and see if it works"
"Add multiple changes, run tests"
"Skip the test, I'll manually verify"
"It's probably X, let me fix that"
"I don't fully understand but this might work"
"Pattern says X but I'll adapt it differently"
"Here are the main problems: [lists fixes without investigation]"
Proposing solutions before tracing data flow
"One more fix attempt" (when already tried 2+)
Each fix reveals new problem in different place

ALL of these mean: STOP. Return to Phase 1.

If 3+ fixes failed: Question the architecture (not just symptoms)

Topic Guides

📖 @references/systematic.md - Four-Phase Framework

Complete systematic debugging process
Phase 1: Root cause investigation
Phase 2: Pattern analysis
Phase 3: Hypothesis and testing
Phase 4: Implementation
Multi-component system diagnostics
3+ fix failure → architectural questioning
Human partner signals you're doing it wrong
Common rationalizations to avoid

🔍 @references/root-cause.md - Backward Tracing

Trace bugs backward through call stack
Finding original trigger vs fixing symptoms
Adding stack trace instrumentation
Finding which test causes pollution
Real example: empty projectDir

🛡️ @references/defense-in-depth.md - Multi-Layer Validation

Validate at EVERY layer data passes through
Layer 1: Entry point validation
Layer 2: Business logic validation
Layer 3: Environment guards
Layer 4: Debug instrumentation
Making bugs structurally impossible

✅ @references/verification.md - Evidence Before Claims

The Iron Law: No completion claims without fresh verification
The Gate Function (5 steps before any claim)
Common failures and red flags
Regression test red-green cycle
Why this matters (trust, quality, honesty)

Common Patterns

Multi-Component Diagnostic

# Layer 1: Workflow
echo "=== Secrets available in workflow: ==="
echo "VAR: ${VAR:+SET}${VAR:-UNSET}"

# Layer 2: Build script
echo "=== Env vars in build script: ==="
env | grep VAR || echo "VAR not in environment"

# Layer 3: Target script
echo "=== State at execution: ==="
./script.sh --verbose

# Reveals: Which layer fails

Stack Trace Addition

// Before problematic operation
async function operation(param: string) {
  const stack = new Error().stack;
  console.error('DEBUG operation:', {
    param,
    cwd: process.cwd(),
    env: process.env.NODE_ENV,
    stack,
  });
  
  await doRiskyThing(param);
}

Defense-in-Depth Pattern

// Layer 1: Entry validation
function createThing(path: string) {
  if (!path || path.trim() === '') {
    throw new Error('path cannot be empty');
  }
  
  // Layer 2: Business logic
  if (!existsSync(path)) {
    throw new Error(`path does not exist: ${path}`);
  }
  
  // Layer 3: Environment guard
  if (process.env.NODE_ENV === 'test') {
    if (!path.startsWith(tmpdir())) {
      throw new Error('Test operations must use temp dir');
    }
  }
  
  // Layer 4: Debug instrumentation
  logger.debug('Creating thing', { path, caller: new Error().stack });
  
  // Now safe to proceed
}

Integration

This skill works with:

systematic-thinking - Deep analysis for complex bugs
code-review - Catch bugs before they ship
validate-plan - Ensure fix approach is sound

Real-World Impact

From debugging sessions:

Systematic approach: 15-30 minutes to fix
Random fixes approach: 2-3 hours of thrashing
First-time fix rate: 95% vs 40%
New bugs introduced: Near zero vs common

The Bottom Line:

Find root cause BEFORE proposing fixes
Trace backward to original trigger
Validate at EVERY layer
Verify BEFORE claiming success

This is non-negotiable.

debugging

Systematic Debugging

Core Principle

The Iron Law

When to Use