Debugging with AI

The AI Debugging Mindset

Most developers use AI debugging wrong: they paste an error and say "fix this." That gets you a patch, not an understanding. The right approach is to use AI to understand first, fix second.

Stack Trace Reading

// Paste the full stack trace — not just the last line
// Bad: "I get a TypeError, help"
// Good: paste everything below

Prompt template:
"I'm getting this error in my [Node/Python/Go] app.
Here's the full stack trace:

[paste full stack trace]

Here's the code at the relevant line:

[paste the function or file]

Explain:
1. What is the root cause?
2. Why does this happen?
3. What's the fix?
4. How do I prevent this class of error in future?"

// Example output from Claude:
// Root cause: You're calling .json() on a Response object
// that has already been consumed. Response bodies can only
// be read once. You called res.text() earlier in the middleware
// which drained the stream.
// Fix: Clone the response before reading: res.clone().json()
// Prevention: Use a single body-reading method per response,
// or clone immediately after fetch if you need to read twice.

The /fix Command (Copilot)

// Select the broken code → /fix in Copilot Chat
// Copilot reads the selection + error context and suggests a fix

// For better /fix results, first write a comment:
// BUG: This throws "Cannot read properties of undefined"
// when user.profile is null
function getDisplayName(user: User): string {
  return user.profile.firstName + ' ' + user.profile.lastName
}
// Now /fix knows exactly what the bug is

// Copilot suggests:
function getDisplayName(user: User): string {
  if (!user.profile) return user.email ?? 'Unknown User'
  return [user.profile.firstName, user.profile.lastName]
    .filter(Boolean)
    .join(' ') || user.email ?? 'Unknown User'
}

Root Cause Analysis for Hard Bugs

// For intermittent or complex bugs, give more context:

"This function works correctly in unit tests but fails
in production about 1 in 50 requests. Here's the function:

[code]

It's a race condition I think, but I can't reproduce it locally.
The error is: [error message]
The function runs in a serverless environment with concurrent execution.

What are the possible race conditions here?
What would you add to diagnose which one is occurring?"

// Claude identifies:
// 1. Shared mutable state in module scope (the cache object)
//    not protected for concurrent access
// 2. Time-of-check/time-of-use: checking cache.has(key) then
//    reading cache.get(key) are two separate operations
// Suggests: add a mutex or use an atomic read-then-set pattern

Debugging Patterns by Error Type

Claude Code for Debugging Sessions

# Claude Code can read logs, check related files, trace the call chain
> I'm getting this error: [paste error]
  The relevant file is src/services/payment.ts
  Can you trace through the call chain to find the root cause?

# Ask for a reproduction case
> Write a minimal test that reproduces this bug
  so I can debug it without running the full app

# Compare expected vs actual behaviour
> This function should sort users by last login descending.
  Walk through what it actually does and explain the bug.

# Ask for defensive improvements
> Fix the immediate bug, then suggest what defensive
  coding would prevent this entire class of null-pointer
  errors in this service