Ask HN: How are you vibe coding in an established code base?

Here’s how we’re working with LLMs at my startup.

We have a monorepo with scheduled Python data workflows, two Next.js apps, and a small engineering team. We use GitHub for SCM and CI/CD, deploy to GCP and Vercel, and lean heavily on automation.

Local development: Every engineer gets Cursor Pro (plus Bugbot), Gemini Pro, OpenAI Pro, and optionally Claude Pro. We don’t really care which model people use. In practice, LLMs are worth about 1.5 excellent junior/mid-level engineers per engineer, so paying for multiple models is easily worth it.

We rely heavily on pre-commit hooks: ty, ruff, TypeScript checks, tests across all languages, formatting, and other guards. Everything is auto-formatted. LLMs make types and tests much easier to write, though complex typing still needs some hand-holding.

GitHub + Copilot workflow: We pay for GitHub Enterprise primarily because it allows assigning issues to Copilot, which then opens a PR. Our rule is simple: if you open an issue, you assign it to Copilot. Every issue gets a code attempt attached to it.

There’s no stigma around lots of PRs. We frequently delete ones we don’t use.

We use Turborepo for the monorepo and are fully uv on the Python side.

All coding practices are encoded in .cursor/rules files. For example: “If you are doing database work, only edit Drizzle’s schema.ts and don’t hand-write SQL.” Cursor generally respects this, but other tools struggle to consistently read or follow these rules no matter how many agent.md-style files we add.

My personal dev loop: If I’m on the go and see a bug or have an idea, I open a GitHub issue (via Slack, mobile, or web) and assign it to Copilot. Sometimes the issue is detailed; sometimes a single sentence. Copilot opens a PR, and I review it later.

If I’m at the keyboard, I start in Cursor as an agent in a Git worktree, using whatever the best model is. I iterate until I’m happy, ask the LLM to write tests, review everything, and push to GitHub. Before a human review, I let Cursor Bugbot, Copilot, and GitHub CodeQL review the code, and ask Copilot to fix anything they flag.

Things that are still painful: To really know if code works, I need to run Temporal, two Next.js apps, several Python workers, and a Node worker. Some of this is Dockerized, some isn’t. Then I need a browser to run manual checks.

AFAICT, there’s no service that lets me: give a prompt, write the code, spin up all this infra, run Playwright, handle database migrations, and let me manually poke at the system. We approximate this with GitHub Actions, but that doesn’t help with manual verification or DB work.

Copilot doesn’t let you choose a model when assigning an issue or during code review. The model it uses is generally bad. You can pick a model in Copilot chat, but not in issues, PRs or reviews.

Cursor + worktrees + agents suck. Worktrees clone from the source repo including unstaged files, so if you want a clean agent environment, your main repo has to be clean. At times it feels simpler to just clone the repo into a new directory instead of using worktrees.

What’s working well: Because we constantly spin up agents, our monorepo setup scripts are well-tested and reliable. They also translate cleanly into CI/CD.

Roughly 25% of “open issue → Copilot PR” results are mergeable as-is. That’s not amazing, but better than zero, and it gets to ~50% with a few comments. This would be higher if Copilot followed our setup instructions more reliably or let us use stronger models.

Overall, for roughly $1k/month, we’re getting the equivalent of 1.5 additional junior/mid engineers per engineer. Those “LLM engineers” always write tests, follow standards, produce good commit messages, and work 24/7. There’s friction in reviewing and context-switching across agents, but it’s manageable.

What are you doing for vibe coding in a production system?

10 points | by adam_gyroscope 1 day ago

4 comments

  • dazamarquez 1 day ago
    I use AI to write specific types of unit tests, that would be extremely tedious to write by hand, but are easy to verify for correctness. That aside, it's pretty much useless. Context windows are never big enough to encompass anything that isn't a toy project, and/or the costs build up fast, and/or the project is legacy with many obscure concurrently moving parts which the AI isn't able to correctly understand, and/or overall it takes significantly more time to get the AI to generate something passable and double check it than just doing it myself from the get go.

    Rarely, I'm able to get the AI to generate function implementations for somewhat complex but self-contained tasks that I then copy-paste into the code base.

    • sourdoughness 11 hours ago
      Interesting. I treat VScode Copilot as a junior-ish pair programmer, and get really good results for function implementations. Walking it through the plan in smaller steps, noting that we’ll build up to the end state in advance ie. “first let’s implement attribute x, then we’ll add filtering for x later”, and explicitly using planning modes and prompts - these all allow me to go much faster, have good understanding of how the code works, and produce much higher quality (tests, documentation, commit messages) work.

      I feel like, if a prompt for a function implementation doesn’t produce something reasonable, then it should be broken down further.

      I don’t know how others define “vibe-coding”, but this feels like a lower-level approach. On the times I’ve tried automating more, letting the models run longer, I haven’t liked the results. I’m not interested in going more hands-free yet.

  • Sevii 1 day ago
    Can you setup automated integration/end-to-end tests and find a way to feed that back into your AI agents before a human looks at it? Either via an MCP server or just a comment on the pull request if the AI has access to PR comments. Not only is your lack of an integration testing pipeline slowing you down, it's also slowing your AI agents down.

    "AFAICT, there’s no service that lets me"... Just make that service!

    • adam_gyroscope 14 hours ago
      We do integration testing in a preview/staging env (and locally), and can do it via docker compose with some GitHub workflow magic (and used to do it that way, but setup really slowed us down).

      What I want is a remote dev env that comes up when I create a new agent and is just like local. I can make the service but right now priorities aren’t that (as much as I would enjoy building that service, I personally love making dev tooling).

  • bitbasher 1 day ago
    I generally vibe code with vim and my playlist in Cmus.
    • adam_gyroscope 14 hours ago
      Man I was vim for life until cursor and the LLMs. For personal stuff I still do claude + vim because I love vim. I literally met my wife because I had a vim shirt on and she was an emacs user.
  • jemiluv8 7 hours ago
    Your setup is interesting. I’ve had my mind on this space for a while now but haven’t done any deep work on a setup that optimizes the things I’m interested in.

    I think at a fundamental level, I expect we can produce higher quality software under budget. And I really liked how you were clearly thinking about cost benefits especially in your setup. I’ve encountered far too many developers that just want to avoid as much cognitive work as possible. Too many junior and mid devs also are more interested in doing as they are told instead of thinking about the problem for themselves. For the most part, in my part of the world at least, junior and mid-level devs can indeed be replaced by a claude code max subscription of around $200 per month and you’d probably get more done in a week than four such devs that basically end up using an llm to do work that they might not even thoroughly explore.

    So in my mind I’ve been thinking a lot about all aspects of the Software Development LifeCycle that could be improved using some llm or sorts.

    ## Requirements. How can we use llms to not only organize requirements but to strip them down into executable units of work that are sequenced in a way that makes sense. How do we go further to integrate an llm into our software development processes - be it a sprint or whatever. In a lot of green field projects, after designing the core components of the system, we now need to create tasks, group them, sequence them and work out how we go about assigning them and reviewing and updating various boards or issue trackers or whatever. There is a lot of gruntwork involved in this. I’ve seen people use mcps to automatically create tasks in some of these issue trackers based on some pdf of the requirements together with a design document.

    ## Code Review - I effectively spend 40% of my time reviewing code written by other developers and I mostly fix the issues I consider “minor” - which is about 60% of the time. I could really spend less time reviewing code with the help of an llm code reviewer that simply does a “first pass” to at least give me an idea of where to spend more of my time - like on things that are more nuanced.

    ## Software Design - This is tricky. Chatbots will probably lie to you if you are not a domain expert. You mostly use them to diagnose your designs and point out potential problems with your design that someone else would’ve seen if they were also domain experts in whatever you were building. We can explore a lot of alternate approaches generated by llms and improve them.

    ## Bugfixes - This is probably a big win for llms’ because there used to be a platform where I used to be able to get $50s and $30s to fix github bugs - that have now almost entirely been outsourced to llms. For me to have lost revenue in that space was the biggest sign of the usefulness of llms I got in practice. After a typical greenfield project has been worked on for about two months, bugs start creeping in. For apps that were properly architected, I expect these bugs to be fixable by existing patterns throughout the codebase. Be it removing a custom implementation to use a shared utility or other or simply using the design systems colors instead of a custom hardcoded one. In fact for most bugs - llms can probably get you about 50% of the way most of the time.

    ## Writing actual (PLUMBING) code . This is often not as much of a bottleneck as most would like to think but it helps when developers don’t have to do a lot of the grunt-work involved in creating source files, following conventions in a codebase, creating boilerplates and moving things around. This is an incredible use of llms that is hardly mentioned because it is not that “hot”.

    ## Testing - In most of the projects we worked on at a consulting firm, writing tests - whether ui or api was never part of the agreement because of the economics of most of our gigs. And the clients never really cared because all they wanted was working software. For a developing firm however, testing can be immense especially when using llms. It can provide guardrails to check when a model is doing something it wasn’t asked to do. And can also be used to create and enforce system boundaries especially in pseudo type systems like Typescript where JavaScript’s escape hatches may be used as a loophole.

    ## DEVOPS. I remember there was a time we used to manually invalidate cloudfront distributions after deploying our ui build to some e3 bucket. We’ve subsequently added a pipeline stage to invalidate the distribution. But I expect there are lots of grunt devops work that could really be delegated. Of course, this is a very scary use of llms but I daresay - we can find ways to use it safely

    ## OBSERVABILITY - a lot of observability platforms already have this feature where llms are able to review error logs that are ingested, diagnose the issue, create an issue on github or Jira (or wherever), create a draft PR, review, test it in some container, iterate on a solution X times, notify someone to review and so on and so forth. Some llms on this observability platform also attach a level of priority and dispatch messages to relevant developers or teams. LLms in this loop simply supercharge the whole observability/instrumentation of production applications

    But yeah, that is just my two cents. I don’t have any answers yet I just ponder on this every now and then at a keyboard.