An AI agent coding skeptic tries AI agent coding, in excessive detail | Max Woolf’s Blog

You’ve likely seen many blog posts about AI agent coding/vibecoding where the author talks about all the wonderful things agents can now do supported by vague anecdata, how agents will lead to the atrophy of programming skills, how agents impugn the sovereignty of the human soul, etc etc. This is NOT one of those posts. You’ve been warned.

In November, just a few days before Thanksgiving, Anthropic released Claude Opus 4.5 and naturally my coworkers were curious if it was a significant improvement over Sonnet 4.5. It was very suspicious that Anthropic released Opus 4.5 right before a major holiday since companies typically do that in order to bury underwhelming announcements as your prospective users will be too busy gathering with family and friends to notice. Fortunately, I had no friends and no family in San Francisco so I had plenty of bandwidth to test the new Opus.

One aspect of agents I hadn’t researched but knew was necessary to getting good results from agents was the concept of the AGENTS.md file: a file which can control specific behaviors of the agents such as code formatting. If the file is present in the project root, the agent will automatically read the file and in theory obey all the rules within. This is analogous to system prompts for normal LLM calls and if you’ve been following my writing, I have an unhealthy addiction to highly nuanced system prompts with additional shenanigans such as ALL CAPS for increased adherence to more important rules (yes, that’s still effective). I could not find a good starting point for a Python-oriented AGENTS.md I liked, so I asked Opus 4.5 to make one:

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