v2026.1CASRAI Dictionary 714 entries across 20 domains · CC-BY 4.0714 entries · CC-BY 4.0

Dictionary termTrack AStablev2026.2

System prompt

A prompt provided to an LLM at the start of a session — typically not visible to the end user — that sets persona, constraints, output format, safety rules, and tool-use permissions for all subsequent user interactions in that session.

ByCASRAI Editorial Board

· Last updated 21 May 2026

Examples

Worked examples

Is an instance
A custom GPT configured with the system prompt 'You are a biostatistician. Always ask about study design before suggesting tests.'

Counter-examples

Looks similar, but isn't

Not an instance
A user typing instructions into the chat window during a session is a user prompt, not a system prompt

Editorial commentary

Distinct from user prompts in that it conditions the model’s behaviour across the whole conversation. When an AI tool is used in research, the system prompt is part of the reproducibility envelope: two researchers issuing identical user prompts to the same model may get different outputs if the system prompts differ.

References

Anthropic System Prompt documentation (2024)
OpenAI API Reference (2024)

Also known as

Developer prompt · Pre-prompt

Machine-readable encodings

Use in your systems

JATS XML <role> element

xml

<role vocab="credit"
      vocab-identifier="https://casrai.org/dictionary/"
      vocab-term="System prompt"
      vocab-term-identifier="https://casrai.org/dictionary/term/system-prompt" />

Schema.org DefinedTerm (JSON-LD)

json

{
  "@context": "https://schema.org",
  "@type": "DefinedTerm",
  "name": "System prompt",
  "identifier": "https://casrai.org/dictionary/term/system-prompt",
  "description": "A prompt provided to an LLM at the start of a session — typically not visible to the end user — that sets persona, constraints, output format, safety rules, and tool-use permissions for all subsequent user interactions in that session.",
  "inDefinedTermSet": "https://casrai.org/dictionary/domain/generative-ai-use-and-disclosure/",
  "url": "https://casrai.org/dictionary/term/system-prompt",
  "sameAs": [
    "Developer prompt",
    "Pre-prompt"
  ],
  "license": "https://creativecommons.org/licenses/by/4.0/"
}

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