System prompt
A system prompt is the standing instruction given to a model ahead of every request. It sets the agent's role, tone, boundaries and rules before any user has said a word, and it stays in force for the whole interaction. Where a user's prompt is the question of the moment, the system prompt is the brief the agent always works to.
A useful way to see it: the user prompt is what you ask, the system prompt is who you are asking. The same model can behave like a formal support agent, a concise analyst or a friendly assistant purely by changing its system prompt.
The system prompt is sent on every request and shares the context window with everything else, but the end user does not see it. It is set once, in configuration, rather than written anew for each message.
What a system prompt typically covers​
- Role and purpose: what the agent is for and who it serves.
- Tone and style: how it should speak.
- Boundaries: what it should refuse, avoid, or escalate.
- How to use its knowledge and tools: when to retrieve, cite, or take an action.
The system prompt in Rational AI​
The system prompt is one of the ingredients a touchpoint binds together, alongside its model, knowledge and tools. It is what turns a general‑purpose model into a purpose‑built agent for one job, and changing it changes how that touchpoint behaves without affecting any other.