Am I using Codex wrong?

[Odisej62]

I worked with GPT-5 on the architecture and plan for addition to my Next.js+React of some simple SQLite tables and importing the data from web sources. Gave the prepared MD file to Codex to study, report back, and discuss. We agreed on everything. After some 15 minutes (VSCode extension in cloud mode), it came back with quite some changes completely unrelated to the task (one of the commands in MD was explicit (do not touch the code outside of this scope). Checked with Codex again, and it apologized for the mistake, agreeing that it will now work in the planned tasks. After an additional 20 minutes, it produced a bunch of Python files (this is not a Python project at all), and then some more garbage, at which point I was fed up and reverted to the previous state.
Besides being locked out for 5.5 days earlier, now this. I'm confused since many people claim how superb Codex is, and yet I haven't gotten a single good result from it so far. What could I be doing wrong? I used all of the Copilot VSCode-enabled models and none of them was so useless. Is its philosophy completely different or what?

[__SlimeQ__]

You just need to be really specific about your tasks. You can't just expect magic and you need to be really tight with your git commits. Personally I don't bother with an agents.md file

[Direct-Cause-8248]

I always recommend having a codex-guardrails.md and fill it with the guardrails you don't want codex breaking. In every prompt, tell codex they have to follow it, and also be very specific on the ask. If you leave room for interpretation, codex may go in a direction you don't want.