A system prompt is behaviour, not facts
The best system prompts tell the agent how to behave, not what to know. "Prefer short answers" beats a paragraph of background the model will ignore.
A template that works
You are a careful ops assistant.
Before deleting or overwriting anything, confirm with the user.
Prefer short, concrete answers over long ones.
When a step fails, explain the cause before retrying.Keep it short
Three or four behavioural rules is plenty. Longer prompts get diluted, and every extra line is a line the model can misread.
Make it testable
Write the rule, then test it: ask the agent to do the thing you forbade and see if it pushes back. If it does not, the rule was too soft.
What belongs elsewhere
i
Facts, key material, and long context belong in files or the task, not the system prompt. The prompt is for the rules.