System Prompt
Definition
A system prompt is the hidden or privileged instruction layer that steers a model’s role, rules, and style before the user’s messages are applied.
By Vinespire Editorial Team, Editorial ·
This term is part of the full AI search glossary.
Full definition
Chat APIs and products typically separate system (or developer) instructions from user and assistant turns. The system prompt may define persona, safety policies, output format, tool-use rules, and what the model should refuse. Users often cannot see or edit the full system layer in consumer apps.
System prompts shape answer behavior globally—how citations are presented, whether the model admits uncertainty, or how it handles brand comparisons—but they do not replace public web evidence for grounded products.
Custom GPTs, enterprise assistants, and agent frameworks rely heavily on system-style instructions plus optional knowledge files. See Prompt, Custom GPT, and Project Knowledge.
Example
A support bot’s system prompt requires concise answers, mandatory links to official docs, and refusal of legal advice outside a fixed FAQ set.