Claude Code Workflow: Bug Fixing

The Bug Fixing Workflow

Bug fixing is where Claude Code shines brightest. Instead of manually tracing through files, you hand Claude the error and let it do the detective work.

Step 1: Paste the Error

Start simple. Give Claude the raw error output:

"I'm getting this error when I try to submit the contact form:

TypeError: Cannot read properties of undefined (reading 'email')
  at POST /api/contact (src/app/api/contact/route.ts:12:28)
"

Claude reads the stack trace, opens the file, and traces the data flow to find the root cause.

Step 2: Let Claude Investigate

Claude typically:

1. Reads the file mentioned in the stack trace
2. Traces the variable back to where it's defined
3. Checks the request/response types
4. Identifies the mismatch

You'll see Claude working through the problem step by step. Resist the urge to interrupt — let it finish its analysis.

Step 3: Review the Fix

Claude proposes a fix. Before accepting, check:

• Does the fix address the root cause? Not just the symptom
• Are there other places with the same bug? Ask Claude: "Are there other endpoints with the same pattern?"
• Does it handle edge cases? "What if email is an empty string?"

Real Example: The Undefined Body Bug

Here's a bug we hit on this very site:

// ❌ Bug: body might be undefined if Content-Type header is missing
export async function POST(req: Request) {
  const { email } = await req.json();
  // ...
}

The fix:

// ✅ Fix: validate the request body exists
export async function POST(req: Request) {
  let body;
  try {
    body = await req.json();
  } catch {
    return Response.json(
      { error: "Invalid request body" },
      { status: 400 }
    );
  }

  const { email } = body;
  if (!email || typeof email !== "string") {
    return Response.json(
      { error: "Email is required" },
      { status: 400 }
    );
  }
  // ...
}

Step 4: Verify the Fix

Ask Claude to run your tests:

"Run the tests for the contact API endpoint"

If there aren't tests yet:

"Write tests for this endpoint covering: valid submission, missing email, invalid JSON body, and empty string email"

Workflow Tips

• Copy the full error — Including the stack trace. More context = better diagnosis
• Mention what you've tried — "I already checked that the env var is set" saves Claude from going down the same path
• Ask for the why — "Why was this undefined?" Understanding the cause prevents recurrence
• Check for patterns — "Are there other places in the codebase with the same issue?" Claude can grep for similar patterns