At my dayjob my team uses it on our main dashboard, which is a pretty large CRUD application. The frontend (Vue) is a horrible mess, as it was originally built by people who know just enough to be dangerous. Over time people have introduced new standards without cleaning up the old code - for example, we have three or four different state management techologies.

For this the LLM struggles a bit, but so does a human. The main issues are it messes up some state that it didnt realise was used elsewhere, and out test coverage is not great. We've seen humans make exactly the same kind of mistakes. We use MCP for Figma so most of the time it can get a UI 95% done, just a few tweaks needed by the operator.

On the backend (Typescript + Node, good test coverage) it can pretty much one-shot - from a plan - whatever feature you give it.

We use opus-4.5 mostly, and sometimes gpt-5.2-codex, through Cursor. You aren't going to get ChatGPT (the web interface) to do anything useful, switch to Cursor, Codex or Claude Code. And right now it is worth paying for the subscription, you don't get the same quality from cheaper or free models (although they are starting to catch up, I've had promising results from GLM-4.7).