Debugging & Explaining Code

Debugging Code with ChatGPT

Debugging is often more frustrating than writing code in the first place. You have a bug you can't find, an error message that's not helpful, or code that behaves differently than you expect. ChatGPT is a remarkably effective debugging partner — not because it magically knows the answer, but because explaining a bug clearly is often half of solving it, and ChatGPT forces you to do that.

The Core Debugging Prompt

The best debugging prompts include everything ChatGPT needs to actually diagnose the problem:

I have a bug and I need help diagnosing it.

**What I'm trying to do:**
[Describe the expected behavior]

**What's actually happening:**
[Describe the actual behavior — be specific]

**Error message (if any):**
[Paste the full error, including the stack trace]

**Relevant code:**
[Paste the minimal code that reproduces the issue]

**What I've already tried:**
[List the things you've already ruled out]

**Environment:**
[Language version, framework version, OS if relevant]

The more of this context you provide, the better the diagnosis. Don't make ChatGPT play 20 questions by leaving out obvious information.

Pasting Error Messages

Always paste the complete error, including the stack trace:

I'm getting this error in my Next.js app. What does it mean and how do I fix it?

Error:
TypeError: Cannot read properties of undefined (reading 'map')
    at CourseList (src/components/CourseList.tsx:23:18)
    at renderWithHooks (node_modules/react-dom/cjs/react-dom.development.js:14985:18)
    ...

Here's the component at that line:
[paste component code]

The data comes from this server action:
[paste server action code]

The stack trace tells ChatGPT exactly where to look. Without it, the diagnosis is much less reliable.

Diagnosing "It Works in Dev but Not in Production"

This category of bug has a specific set of likely causes. Ask about them explicitly:

My code works locally but fails in production. 

Error: [paste error]
Environment difference: [Next.js on Vercel, Node.js version, etc.]

Help me systematically diagnose this. What are the most common causes of this 
specific error in a production Next.js deployment, ranked by likelihood?

Then, for each cause, tell me how to confirm or rule it out.

Common production-only bugs: environment variables not set, Node.js version mismatch, file system differences, edge runtime limitations, build-time vs. runtime behavior.

Debugging with Minimal Reproducible Examples

When code is complex, isolate the problem:

I have a bug in a large component. I've isolated it to this minimal example 
that still reproduces the issue:

[paste minimal reproduction]

Expected behavior: [describe]
Actual behavior: [describe]

What's wrong with this code?

Creating a minimal reproduction yourself is good debugging practice — and it often leads you to discover the bug before you even ask.

Async and Timing Bugs

These are notoriously hard to spot because the code looks correct:

I have a race condition or async bug. The code works most of the time 
but sometimes fails unpredictably.

Code:
[paste relevant async code]

What I think is happening: [your hypothesis]

Review this for:
1. Race conditions (two async operations modifying shared state)
2. Missing awaits
3. Unhandled promise rejections
4. setState calls after component unmount
5. Any other async pitfalls you can spot

TypeScript Type Errors

TypeScript error messages can be cryptic. Paste them in with the code:

TypeScript is giving me this error and I don't understand it:

Error:
Type 'string | undefined' is not assignable to type 'string'.
  Type 'undefined' is not assignable to type 'string'.

At this line:
[paste the line and surrounding context]

Here's the full relevant code:
[paste code]

Explain:
1. What exactly is TypeScript telling me?
2. Why is this a problem?
3. What's the right fix (and if there are multiple approaches, explain the tradeoffs)?

Debugging Performance Problems

When something is slow:

This function is too slow. It takes ~2 seconds on a dataset of 10,000 items.

[paste function code]

Analyze this for performance issues. What's the algorithmic complexity?
What are the most likely bottlenecks?
How would you rewrite this to be faster?

Constraints:
- The output must be identical
- Can't use external libraries (only built-in JavaScript/Node.js)

Systematic Debugging with ChatGPT

When you genuinely don't know where to start:

I have a bug I can't locate. Here's what I know:

**Symptom:** [what goes wrong]
**When it happens:** [conditions — always? random? specific input?]
**When it doesn't happen:** [conditions when it works]
**What I've ruled out:** [what you've already checked]

Codebase context:
[brief description of the system: framework, key files involved]

Give me a systematic debugging strategy. What should I check first, 
second, and third? What logging should I add to narrow down the location?

The "Explain This Error to Me" Prompt

Sometimes you just need the error demystified:

Explain this error message to me in plain language:

[paste error]

I want to understand:
1. What is actually failing?
2. What is the root cause (not just the symptom)?
3. What are the most common reasons this error occurs?
4. How do I fix each possible cause?

Debugging API and Network Issues

When working with HTTP APIs:

My API call is failing and I don't understand why.

Request I'm making:
[method, URL, headers, body]

Response I'm getting:
[status code, response body]

Expected response:
[what should come back]

Here's the relevant code:
[paste fetch/axios/whatever code]

What could cause this? What should I check?

For 401/403 errors: authentication headers, token format, token expiry For 404 errors: URL path, query parameters, whether the endpoint exists For 500 errors: server-side error, check server logs

When ChatGPT Gives a Wrong Fix

This happens. The model is confident about wrong answers sometimes. When a suggested fix doesn't work:

I tried your suggested fix and it didn't work.

Here's what happened when I applied it:
[describe what changed and what error/behavior occurred]

Updated code after applying your fix:
[paste updated code]

New error (if any):
[paste new error]

Let's try a different approach. What else could be causing this?

Re-orienting ChatGPT with the failure result usually produces better second attempts.

Building Debugging Skills

ChatGPT is a useful crutch — but use it to build your skills, not replace them:

I've found the bug — here it was: [explain what was wrong]

Help me understand WHY this caused the behavior I was seeing.
What should I have looked for first to find this faster?
What pattern or principle would have led me to this bug more quickly?

Learning the "why" behind each bug makes you a faster debugger over time.

Next lesson: Writing tests and documentation — using ChatGPT to build quality into your code.