Vibe-coded startup before the funding round: what investors really check under the hood

Your product works. Users pay, the numbers add up, the first investor conversation looks promising. Then comes the sentence that catches many AI-built startups off guard: “Can we take a look at the code?”

And suddenly the question is no longer whether the product works - it visibly does. The question is what sits beneath the surface. That is exactly what technical due diligence examines. And it examines something different from your demo.

Why investors now ask about the AI share

A large part of early startup codebases today is written with AI, no longer line by line by hand. That is not a flaw, it is the new normal - and that is precisely why investors now look closely. Not to punish AI, but because “built fast” and “built to last” are two different things.

The point many founders underestimate: an investor is not buying what the product does today. They are buying the probability that a team can still run, extend and scale it safely in two years. A codebase that nobody on the team can fully explain lowers exactly that probability. It shows up in the valuation long before anyone says the words “security hole.”

The red flags are not bugs, they are structure

If you think the review is about clever mistakes, you are wrong. What stands out is usually mundane - and that is exactly what makes it telling:

• No tests. If nothing automatically checks whether a change breaks something, every next step is a blind flight.
• Hardcoded secrets. API keys, passwords, tokens directly in the code or the repository. The most common, most expensive and most embarrassing finding.
• No traceable architecture. If every function is solved differently because it was generated in a different session, nobody can reliably change the logic.
• Bus factor of one. Nobody can explain the codebase end to end. With hand-grown code at least the author knows it. With purely prompt-based builds, often: nobody.

None of these points mean your product is bad. They mean the path from prototype to a durable system has not been walked yet. A reviewer sees the difference in minutes.

The most dangerous moment for a gap

There is one moment when a security hole does maximum damage: when the investor finds it, not you. There have been public cases where exactly that happened - a leak exposed right around a funding round. The technical damage is then often the smaller problem. The bigger one is the signal: if that slipped through, what else is unreviewed?

The same gap you find and close yourself beforehand is a footnote. The same gap that surfaces in screening is a lever against you.

What you can check yourself in advance

Full due diligence is an outside view - more on that in a moment. But the obvious third you can clear yourself:

• Is any key, password or token sitting in the code or the git history? (Deleted counts too - the history stays.)
• Are there tests at all, and do they run?
• Are your endpoints protected, or can anyone with the right URL pull data?
• Is personal data handled cleanly - GDPR-compliant, not just “it works”?
• Can one person on the team explain the architecture in half an hour?

Whoever honestly ticks four of five here walks into the conversation a lot calmer.

What real preparation looks like

The fifth point you cannot tick yourself - you do not review your own codebase objectively. That is not distrust, it is the same reason nobody runs their own tax return as the audit. An external technical review looks with the investor’s eyes: security, data protection, structure, maintainability, scalability - and hands you the findings before the other side does.

The goal is not to hide the AI share. On the contrary: having built fast with AI is an advantage, as long as the result has been reviewed. The goal is that when you hear “Can we take a look at the code?” you do not swallow - you nod.

I build with AI myself - and I make the results production-ready and reviewable. When your round moves closer, the best time for an honest look at the code is while you are still the one ordering it, not the investor.