Debugger

Debugger

An advanced debugging specialist that helps diagnose and resolve code issues systematically.

When This Skill Activates

Activates when you:

• Report an error or bug
• Mention "debug this" or "help debug"
• Describe unexpected behavior
• Ask why something isn't working

Debugging Process

Phase 1: Understand the Problem

1. Reproduce the issue

• What are the exact steps to reproduce?
• What is the expected behavior?
• What is the actual behavior?
• What error messages appear?

2. Gather context

   # Check recent changes
   git log --oneline -10

   # Check error logs
   tail -f logs/error.log

   # Check environment
   env | grep -i debug

Phase 2: Isolate the Issue

1. Locate the error source

• Stack trace analysis
• Error code lookup
• Log correlation

2. Narrow down scope

• Binary search (comment out half)
• Minimize reproduction case
• Identify affected components

Phase 3: Analyze the Root Cause

Common Error Categories

Phase 4: Form Hypotheses

For each potential cause: 1. Form a hypothesis 2. Create a test to validate 3. Run the test 4. Confirm or reject

Phase 5: Fix and Verify

1. Implement the fix 2. Add logging if needed 3. Test the fix 4. Add regression test

Debugging Commands

General Debugging

# Find recently modified files
find . -type f -mtime -1 -name "*.js" -o -name "*.ts" -o -name "*.py"

# Grep for error patterns
grep -r "ERROR\|FATAL\|Exception" logs/

# Search for suspicious patterns
grep -r "TODO\|FIXME\|XXX" src/

# Check for console.log left in code
grep -r "console\.log\|debugger" src/

Language-Specific

JavaScript/TypeScript:

# Run with debug output
NODE_DEBUG=* node app.js

# Check syntax
node -c file.js

# Run tests in debug mode
npm test -- --inspect-brk

Python:

# Run with pdb
python -m pdb script.py

# Check syntax
python -m py_compile script.py

# Verbose mode
python -v script.py

Go:

# Race detection
go run -race main.go

# Debug build
go build -gcflags="-N -l"

# Profile
go test -cpuprofile=cpu.prof

Common Debugging Patterns

Pattern 1: Divide and Conquer

# When you don't know where the bug is:
def process():
    step1()
    step2()
    step3()
    step4()

# Comment out half:
def process():
    step1()
    # step2()
    # step3()
    # step4()

# If bug disappears, uncomment half of commented:
def process():
    step1()
    step2()
    # step3()
    # step4()

# Continue until you isolate the bug

Pattern 2: Add Logging

// Before (mysterious failure):
async function getUser(id: string) {
  const user = await db.find(id);
  return transform(user);
}

// After (with logging):
async function getUser(id: string) {
  console.log('[DEBUG] getUser called with id:', id);
  const user = await db.find(id);
  console.log('[DEBUG] db.find returned:', user);
  const result = transform(user);
  console.log('[DEBUG] transform returned:', result);
  return result;
}

Pattern 3: Minimal Reproduction

// Complex code with bug:
function processBatch(items, options) {
  // 100 lines of complex logic
}

// Create minimal reproduction:
function processBatch(items, options) {
  console.log('Items:', items.length);
  console.log('Options:', options);
  // Test with minimal data
  return processBatch([items[0]], options);
}

Error Message Analysis

Common Error Messages

Debugging Checklist

• [ ] I can reproduce the issue consistently
• [ ] I have identified the exact error location
• [ ] I understand the root cause
• [ ] I have a proposed fix
• [ ] The fix doesn't break existing functionality
• [ ] I've added a test to prevent regression

Scripts

Generate a debug report:

python scripts/debug_report.py <error-message>

References

• references/checklist.md - Debugging checklist
• references/patterns.md - Common debugging patterns
• references/errors.md - Error message reference

Debugger

A Claude Code skill for systematic debugging and issue resolution.

Installation

This skill is part of the agent-playbook collection.

Usage

When encountering an error or bug:

You: This function is throwing an error
You: Debug this code
You: Why isn't this working?

The skill will: 1. Analyze the error message 2. Trace the root cause 3. Provide debugging steps 4. Suggest fixes

Debugging Process

Common Error Types

Scripts

Generate debug report:

python scripts/debug_report.py "<error-message>"

Resources

• Debugging Best Practices
• Systematic Debugging

Debugging Checklist

• [ ] Reproduce the issue
• [ ] Isolate the failure
• [ ] Identify root cause
• [ ] Implement fix
• [ ] Add regression coverage

Common Error Types

• Null/undefined access
• Race conditions
• Configuration mismatches
• Data shape drift

Debugging Patterns

• Binary search the change set
• Add targeted logging
• Reduce problem scope with minimal repros