I have a medium-sized typescript personal project I work on. It probably has 20k LOC of well organized typescript (react frontend, express backend). I also have somewhat comprehensive docs and cursor project rules.
In general I use Cursor in manual mode asking it to make very well scoped small changes (e.g. “write this function that does this in this exact spot”). Yesterday I needed to make a largely mechanical change (change a concept in the front end, make updates to the corresponding endpoints, update the data access methods, update the database schema).
This is something very easy I would expect a junior developer to be able to accomplish. It is simple, largely mechanical, but touches a lot of files. Cursor agent mode puked all over itself using Gemini 2.5. It could summarize what changes would need to be made, but it was totally incapable of making the changes. It would add weird hard coded conditions, define new unrelated files, not follow the conventions of the surrounding code at all.
TLDR; I think LLMs right now are good for greenfield development (create this front end from scratch following common patterns), and small scoped changes to a few files. If you have any kind of medium sized refactor on an existing code base forget about it.
> Cursor agent mode puked all over itself using Gemini 2.5. It could summarize what changes would need to be made, but it was totally incapable of making the changes.
Gemini 2.5 is currently broken with the Cursor agent; it doesn't seem to be able to issue tool calls correctly. I've been using Gemini to write plans, which Claude then executes, and this seems to work well as a workaround. Still unfortunate that it's like this, though.
Interesting, I’ve found Gemini better than Claude so I defaulted to that. I’ll try another refactor in agent mode with Claude.
My personal opinion is leveraging LLMs on a large code base requires skill. How you construct the prompt, and what you keep in context, which model you use, all have a large effect on the output. If you just put it into cursor and throw your hands up, you probably didnt do it right
I gave it a list of the changes I needed and pointed it to the area of the different files that needed updated. I also have comprehensive cursor project rules. If I needed to hand hold any more than that it would take considerably less time to just make the changes myself.