Vibe CodingAugust 31, 2026·6 min read

How I Use Claude to Debug Logic Before I Write a Single Line of Code

Most bugs aren't code problems. They're thinking problems. Here's how I catch them before they ship.

Most developers debug after the fact. Something breaks, they trace it back, fix it, move on. That cycle is expensive. Not just in time, but in focus. Every context switch to fix a bug is a context switch away from building.

I stopped doing it that way. Now I debug the logic before the code exists. Claude is how I do that.

The Problem With Writing First

When you sit down and start writing code immediately, you're committing to an interpretation of the problem. You've made a hundred small assumptions without realizing it. The data shape, the flow order, the edge cases, the failure states. None of that got validated. You just started building.

Then something breaks at step four because step two had a flawed assumption. And now you're not debugging a bug. You're untangling a web of decisions made while you were in motion.

The fix isn't better code. It's a better thinking process before you write any.

What I Actually Do Instead

Before I open Cursor, before I write a function, I describe what I'm building to Claude like I'm explaining it to a smart engineer who's never seen my codebase. No code. Just logic.

Here's the format I use:

  1. What this thing is supposed to do
  2. What it receives as input
  3. What it should return or trigger as output
  4. The sequence of steps I think it'll take
  5. Where I think it might break

That last one matters most. If I can't name where it might break, I don't understand it well enough to build it yet.

Claude's job in this conversation isn't to write code. It's to poke holes. I explicitly tell it: don't write code yet, just find the problems in this logic.

What Comes Back Is Almost Always Useful

Usually Claude catches one of three things:

A sequence problem. I've got step three depending on something step three can't have yet. Classic async assumption error. Or I'm mutating something before I've verified it exists.

A missing state. I described the happy path. Claude asks what happens when the input is empty, or when the API returns a 200 with an error payload, or when the user hits the endpoint twice before the first call resolves.

A scope creep flag. Sometimes I describe something that's actually three things pretending to be one. Claude will surface that. "This sounds like two separate concerns, do you want them coupled?" That question alone has saved me from building tangled functions I'd have to refactor later.

Why This Works Better Than Rubber Duck Debugging

Rubber ducking works because explaining forces clarity. But the duck doesn't push back. Claude does.

The interactive element is everything. It asks follow-up questions. It makes you be specific. "What does the payload look like?" or "What's the expected behavior if that condition is false?" You can't wave your hands at those. You have to answer.

And answering them out loud, in plain English, usually reveals the gap before you ever touch a keyboard for code.

How I Bring This Into Cursor After

Once the logic review is done, I ask Claude to summarize the approach we landed on. Clean, numbered, plain English. Then I paste that summary as a comment block at the top of the file I'm about to write.

That comment block becomes my spec. Cursor reads it. I read it. If I get lost mid-build, I look up, not back through the chat.

It also gives me something to hand off. If another tool, another model, or a future version of me needs to understand what this function does, the spec is right there. Not buried in a chat log.

The Part That Most People Skip

Asking Claude to find holes in your logic only works if you're specific. Vague prompts get vague responses. "Here's my idea, what do you think?" is not a logic review. That gets you encouragement and surface-level feedback.

The quality of the pre-build review is entirely dependent on how you structure the prompt. And most people don't structure it at all.

The Exact Prompts I Use for Pre-Build Logic Review This is the actual prompt structure I run every time I'm about to build something non-trivial. Copy it, adapt it, make it yours. ...

This section is for Inner Circle members.

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The exact prompts, the edge case extraction format, and how I structure the spec handoff for Cursor are all behind the gate. That's Inner Circle material. If you want the full workflow, that's where it lives.


Keep building

KZZY

Written by KZZY

Kzzy is the founder and CEO of Vaylo Studios. He builds AI-powered software products like Pulse and runs the Inner Circle, teaching operators to build like a giant with a small team.

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