Claude Debugging

You are a Claude Code debugging specialist. The user wants to use Claude Code effectively to diagnose and fix complex issues in their codebase.

What to check first

• Open the Claude Code panel and verify your project files are visible in the file tree
• Check that you have the relevant error message, stack trace, or unexpected behavior description ready to paste
• Confirm which file or function is causing the issue by running the code or checking logs

Steps

1. Paste the exact error message or stack trace into Claude Code — include the full output, not just the first line
2. Reference the specific file path and line number where the issue occurs; use Claude's file explorer to open that file directly
3. Ask Claude to explain what the error means and trace the execution path backward from the error to find the root cause
4. Request Claude generate a minimal reproduction case — a small, isolated code snippet that triggers the bug without dependencies
5. Have Claude identify the specific function or method that contains the bug and explain the logic flaw
6. Ask Claude to suggest a fix with the corrected code; review the logic before applying it
7. Apply the fix to your actual code file using Claude's inline editor or copy the corrected function
8. Run your code again with the same inputs that triggered the original error and confirm the output matches expected behavior

Code

// Minimal debugging workflow in Claude Code
// Example: Finding a bug in array filtering logic

// ORIGINAL BUGGY CODE
function filterActiveUsers(users) {
  return users.filter(user => user.isActive == true);
  // Bug: This filters correctly, but let's say the actual bug is:
  // return users.filter(user => user.isActive); // Missing null check
}

const testUsers = [
  { name: 'Alice', isActive: true },
  { name: 'Bob', isActive: false },
  { name: 'Charlie', isActive: null },
  { name: 'Diana', isActive: undefined }
];

console.log('Buggy output:', filterActiveUsers(testUsers));
// Shows: [{ name: 'Alice', isActive: true }, { name: 'Charlie', isActive: null }]
// Problem: null and undefined are included unexpectedly

// DEBUGGING STEPS IN CLAUDE CODE:
// 1. Ask Claude: "Why does filterActiveUsers include users with null/undefined isActive?"
// 2. Claude explains: "filter(user => user.isActive) uses truthy check, not strict equality"
// 3. Request: "Show me the fixed version with strict boolean checks"

// FIXED CODE
function filterActiveUsers(users) {
  return users.filter(user => user.isActive === true);
}

// VERIFICATION
console.log('Fixed output:', filterActiveUsers(testUsers));
// Shows: [{ name: 'Alice', isActive: true }]
// Correct: Only truly active users included

// DEBUGGING CHECKLIST FUNCTION
function debugCheck(testName, actual, expected) {
  const passed = JSON.stringify(actual) === JSON.stringify(

Note: this example was truncated in the source. See the GitHub repo for the latest full version.

Common Pitfalls

• Treating this skill as a one-shot solution — most workflows need iteration and verification
• Skipping the verification steps — you don't know it worked until you measure
• Applying this skill without understanding the underlying problem — read the related docs first

When NOT to Use This Skill

• When a simpler manual approach would take less than 10 minutes
• On critical production systems without testing in staging first
• When you don't have permission or authorization to make these changes

How to Verify It Worked

• Run the verification steps documented above
• Compare the output against your expected baseline
• Check logs for any warnings or errors — silent failures are the worst kind

Production Considerations

• Test in staging before deploying to production
• Have a rollback plan — every change should be reversible
• Monitor the affected systems for at least 24 hours after the change