Ask HN: How to enforce engineers to understand the code they are shipping

In any case, once the agent session finishes, the constraint file for the next session is written by the same individual. In this case, if the individual didn't read every output line by the agent, he will not know what to include in the new constraint file, leading the agent to make some wrong assumptions about the model, leading to some issues at a certain point in time, which, again, he cannot diagnose because his knowledge of the model is incorrect.

Diff reading is not a practice forced on developers from above. On the contrary, it is the only way for a developer to stay competent enough to lead the next session properly.

Instead of discussing how to ensure that developers will understand the importance of diff reading, the question here is whether the developers understand they cannot shift the responsibility of creating a mental model of the system away from themselves and still maintain effective control over the agent's behavior.

> Company is pushing for AI-first

> But how do we enforce engineers to have a deep understanding of the code that they are shipping?

By not pushing AI-first mindset. When you start tracking token usage metrics, people will optimize for that metric.

If you don't push them, and tell to use AI as a tool, they will optimize for understanding the code

But do we need the level of understanding to be that deep? If you know how your system works overall, how components interact, what interfaces are exposing/consuming, what security, performance implications are there, what data structures carry around... If you have the understanding of that, do you really need to know the actual implementation details? Maybe taking the perspective of a system/product architect is enough?

Having said that, if you want to know if an engineer really gave it a thought before having the AI do the work - you can ask things like "why did you decide to design it like this" - in person

Setup a demo day at the end of each sprint and pick a random developer and ask him to give a complete walkthrough of the code, this will force all the developers to really prepare or actually understand( what they have prompt created) before the demo day. This is atleast I have setup in my corporate job at a Bank in Danmark, I am also building my own startup sekorti.com and forcing myself to do the same(Explain the code to my junior developer before it can be deployed in production).

I think this is company culture. You're asking how to make your engineers give enough of a damn about their output to spend the extra time understanding it.

Did they do this before AI? Does the company really, truly care about software quality or are they just trying to ship features?

Things like

- in depth code reviews

- encouraging sharing knowledge and helping others

- dedicating time to address technical debt

- giving engineers freedom to explore technologies and solutions

- following best practices for software dev

- hiring the right people

This is one of those things you can't enforce, but your leadership can encourage it by setting examples. If your company does not care about understanding the software by carving out time and explicitly encouraging it, then employees won't either.

I find that deeply understanding code is nearly the same level of effort as writing it. That's what I don't really get about AI productivity claims as there is is really only one way to get the coveted 10-100X boost: stop looking at the code.

Of course that is perfect for MVPs, speed runs, getting the general shape of something before you commit to an implementation but for many classes of production code that is too high of a risk to take.

I'd like to hear other's experiences however. Has anyone found a way to get >10X productivity gains with AI in production code with AI?

We also have the problem that a (junior) engineer may not have the skills to understand the AI code.

When you writes code yourself, you only use concepts you have come across previously. But if you generate an AI solution, it may well use concepts one has not previously come across.

What do we expect a junior engineer to do then, if they do not have time to learn the concepts used ? Do we really think they will reject the AI code and implement their own, more familiar, solution ?

AI can do a lot, but engineers still gotta actually know their code. Have them explain it in reviews or docs, do some pair programming, or just walk through their thinking. Tests catch bugs, but understanding comes from being able to justify why stuff exists and how it works. Especially for juniors, this is how they actually level up, AI or not.

You still need other humans to validate and check.

For any design docs, have them do a walkthrough with the team. If they have to speak to their plan live and answer questions, it will be obvious if they've put thought into it or not.

The same thing can be done for any PRs that have some depth to them like if they touch critical logic or involve complexity.

Code reviews don't catch bugs, tests do. AI writes docs fine if your tests work. Juniors learn by shipping, not memorizing patterns. Stop forcing explanations. Build systems that auto-rollback and alert you. That's engineering.Understanding every line is dead. Monitoring and fast feedback matter way more.

I think there are two different problems that get mixed together here:

1. Did the engineer personally understand this change? 2. Is this change allowed to affect critical parts of the system?

The first one is hard to enforce mechanically. You can require design docs, tests, PR explanations, walkthroughs, etc., but a determined person can route all of that through an LLM too.

The second one is more enforceable, and I think it matters a lot in the AI-coding world.

Not all code deserves the same review posture. A dashboard, script, prototype, migration helper, etc. should be able to move fast. But auth, billing, security-sensitive logic, and core business rules should not quietly depend on code that was “just agent output” or barely reviewed.

The pattern I’ve been experimenting with is explicit trust/review tiers in the codebase:

- low-risk / vibe-coded code can exist - agent-touched files get marked as lower-trust - humans can restore trust after review - CI enforces that high-trust code cannot import lower-trust code - critical directories can be required to stay high-trust

This doesn’t prove the engineer understood the code. Nothing really does.

But it does create review memory in the repo. If a file was touched by an agent, that state is visible in the diff. If someone promotes it back to a trusted tier, that promotion is also visible in the diff, and reviewers can ask “did you actually read this?”

I ended up building a small OSS tool around this idea called Tears: https://github.com/Thillel/tears

The slogan is a bit tongue-in-cheek, but it captures the point: vibe-code responsibly.

The framing of "enforce" is the problem. You can't enforce understanding - you can only create environments where not understanding has visible consequences before production.

What works in my experience:

1. Code review with "explain this to me" questions. Not gotchas, genuine "walk me through why this works." If they can't explain it, it doesn't merge.

2. On-call rotation for what you ship. Nothing motivates understanding like being woken up at 3am by your own code.

3. Pair programming on complex features. Not watching - actually driving together.

The real question is: are they shipping code they don't understand because they're lazy, or because the codebase is so complex that nobody fully understands it? If it's the latter, the problem isn't the engineers - it's the architecture.

Add them to the on-call schedule.

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Trying to enforce "deep understanding" is optimizing wrong layer. Focus on: . Fast rollback . Good observability . Small PRs Understanding become emergent, not enforced.