[estebarb]

Simply Ruby on Rails. I maintain 3 markdown documents with system design, implementation plan and use cases in repo. Then tell it those files exist and go implement X feature (from implementation plan). These documents, plus AGENTS.md, declare completion criteria, which includes full code coverage both with system and controller tests.

Usually I don't tell it to implement something adhoc, I first implement it in the documents first. LLMs are quite good to keep those documents in sync.

A good part of the implementation plan is that it keeps the LLM on track. With it, the LLM can understand why something must not be done yet, so it includes less unsolicited functionality. My workflow surely can be improved, but it has worked well for me.

In not sure about the actual costs, because I started using the same subscription for document parsing. But even then, I used less than $10 in may.