What is a system prompt?
A system prompt is a set of instructions a product's developers attach behind every conversation, invisible to the user, that shapes how the model behaves before it ever sees a question.
The company or team building an AI product typically writes a standing set of instructions, covering tone, persona, formatting, what the model should refuse, and which tools it's permitted to use, and sends that alongside every single user prompt. Most users never see this text; it sits behind the scenes and applies the same way to every conversation in that product.
This is a big part of why the same underlying model can feel completely different, or behave completely differently, across products. One app's system prompt might tell the model to search the web for anything time-sensitive; another might tell it to answer only from what it already knows and never cite anything. That instruction, not a difference in the model itself, is often what decides whether a brand mention shows up with a live source attached or as a flat, uncited claim (see mention-vs-citation).
Related
- PromptA prompt is the full text handed to a model right before it responds, and for any real AI product that's almost always more than just what the user typed.
- Tool useTool use is a model's ability to call an outside function mid-answer, such as a search, a calculator, or a code runner, and fold whatever it gets back into its response.
- Web search toolThe web search tool is the specific function that lets an AI assistant fetch and read live web pages mid-conversation, and it's what actually produces a citation rather than a memorized guess.
- Mention vs citationA mention is the model naming you in its answer. A citation is the model linking a source. You can have either without the other, and they mean different things.
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