@3XDataEngg Also, reverse engineering is often the part nobody budgets for. Before you can modernize a system, someone has to figure out what the damn thing actually does xD
@3XDataEngg Business logic definitely changes too, it just tends to get buried in the code, tickets, workarounds, and people’s heads. That’s what makes legacy systems so hard to untangle.
@fjzeit The knowledge-sharing part is still incredibly valuable. Especially on large or legacy systems, the real bottleneck is often that nobody has a shared understanding of how the thing actually works. AI makes generating code cheaper and also makes that missing context more obvious.
@moderneinc Especially interesting to see how a large enterprise tackles this, code review becomes a very different problem at scale. Looking forward to it!
Millions of lines of software are running businesses today, but the people who understand why they work are retiring, leaving, or moving on. Before we rewrite the world's legacy software, we need to understand it.
@sandeeyps Exactly. The code isn't the hard part. The hard part is understanding 10 years of accumulated behavior, dependencies, edge cases and business rules before you touch anything. “Please migrate this without breaking payroll” starts with “please tell me how this actually works.”
@ThePrimeagen This is where “AI writes most of the code” gets dangerous. Without reviewing the existing implementation and slightly different interpretations of the same business logic spread surprisingly fast.. these are the parts which require extensive debugging when they break
@NirmeshMehta@georgemillo Yeah, “figuring out the right behaviour” is exactly it. When a legacy codebase has no clear axis of simplicity, even a good change starts with figuring out how the thing actually works and what you can safely change, and that’s where most of the time goes.
@georgemillo Exactly. The bottleneck isn't just generating good code, rather it's understanding the system well enough to know whether the code is good. On large legacy systems, that context is often scattered across code, APIs, docs, and people's heads.
@0xPascual And that's where AI-assisted modernization gets really interesting: before you ask an agent to change a system, you need a reliable map of how that system actually works. Otherwise you're automating the rewrite and not the understanding that is actually required.
@0xPascual The interesting part isn't that an agent can rewrite 400K tokens overnight, it's whether anyone actually understands what changed. In legacy systems, the hardest problem is reconstructing the behavior, dependencies and business rules you're supposed to preserve.
@zeuslykaios@0x45o The model isn’t getting dumber. The system is giving it terrible context. Years of business rules, dependencies and edge cases are buried in legacy code. A rewrite can clean it up, but unless you understand what the old system does, you’re moving the unknowns around.
@shazcodes He didn’t leave the company with the knowledge. The company left with the knowledge when they let him go. 😭
This is why “we’ll document it later” gets expensive.
@miniii_codes Poor documentation is often just a symptom. Not understanding the system is the real bottleneck. Legacy code, tribal knowledge, and missing docs all add up to the same problem: developers spend hours figuring out what the system doesbefore they can safely change it.
@tunguz Because rewriting isn’t really the hard part, understanding what the existing system does, including all the undocumented edge cases and business rules is. You can’t safely replace what you haven’t mapped yet. That discovery phase is where a lot of rewrite projects get stuck.
@bindureddy The real danger isn't AI writing the code. It's AI changing code nobody understands. If you can't map the existing system and its dependencies, you can't reliably validate what the AI changed. This is exactly the problem we're working on with Scophix.
@VaughnVernon The LOC isn't what scares me here. It's the unknown unknowns between those 3,500 files. 😅 Understanding how one real workflow travels through a system like this is often harder than writing the replacement.
your coding agent has read your entire repo and still doesn't know what your app actually does 🤔
So we made this: record a workflow → get a context file and a workflow diagram mapping real behavior to real code paths
drop it in the repo. agent stops guessing.
we spent weeks reverse engineering a client's codebase because the only person who understood it quit in 2022
never again.
so we built the tool we wished existed: record a workflow, it maps every api call behind it and writes the docs
early access → https://t.co/dF7Up7nhLT