System prompt

A system prompt provides high-priority instructions for a model call: the task, allowed behavior, constraints, tone, and expected output format.

Tiny example

You are a support assistant.
Use only the supplied policy passages.
If the evidence is insufficient, say so.
Return the answer and source IDs.

Important limit

System instructions guide model behavior; they are not a security boundary. They cannot safely replace authentication, authorization, input validation, or tool permissions.

FDE note

Keep the prompt short enough to audit. Put stable policy in tests and application controls, and treat untrusted retrieved text as data rather than instructions.