Prompts and messages
How you talk to a model, and why the system prompt matters.
You talk to a model with messages. The system prompt sets who it is and how it behaves; the user message is the request; the model writes the reply.
System promptExplain things to a 10-year-old in two short sentences, with an everyday example.
UserWhat is recursion?
Model
Recursion is when something calls a copy of itself to solve a smaller piece of a big puzzle. It is like opening a set of Russian nesting dolls, where you keep opening the same toy over and over until you reach the tiniest one inside.
Real replies from gemini-3.5-flash-lite, 2026-10-21
Same model, same question, four very different answers. In an agent, the system prompt is where you write its job and its rules.
Where do you put an agent's rules, like “never refund without approval”?