Put the math in code, the judgment in the spec

When you build an agentic tool, split the work by one question: does this step have a single correct output? If yes, write code. If no, write a spec the agent reads. I have a tool that picks and manages long-dated SPY call options. The split falls out cleanly. The numbers have one right answer, so they live in Python. One script fetches the chain and computes a delta for every contract; another…