A system prompt is the stable configuration for a chat assistant. It defines the role, task, procedures, constraints, output format, and communication style that should carry across interactions. A user prompt supplies the question or data that changes with each request; an assistant message is the model’s response. A system prompt does not run by itself: a conversation needs a user message. section 6.1.2 section 6.2
To split a combined prompt, ask of each part: “Does this configure the system, or does the user provide it?”
- Put role and expertise, task instructions, procedures, boundaries, static background, style, and output specifications in the system prompt. Give it one well-defined responsibility. section 6.2.1 section 6.4.3
- Put the specific request, changing context, input parameters, and documents in the user prompt. Delimit variable content so it is identifiable as data rather than instructions. section 6.1.2 section 6.4.5
- Keep the system prompt static when practical. Separating repeated instructions from variable input also makes standards easier to update; repeated static content may qualify for provider-specific prompt caching. section 6.5 section 6.1.2
Issue-creation assistant
System prompt: “Role: Experienced technical project manager. Task: Turn task descriptions into actionable issues. Constraints: Use professional language; do not invent unsupported implementation details. Output: A title under 10 words, followed by a description covering context, objective, steps, and acceptance criteria.” User prompt: “The homepage search box does nothing when users press Enter. Investigate the cause.” The issue-writing standard stays fixed while each problem report changes. section 6.2.3
Use separate system and user prompts when many requests need identical behavior or instructions need independent maintenance. A combined prompt can be sufficient for a few one-off outputs. Do not repeat system instructions in every user message: repetition creates opportunities for drift. Check constraints for conflicts, too. An instruction to be “as helpful as possible” can undermine a prohibition on disclosing individual records; define the permitted scope explicitly instead. section 6.4.4 section 6.4.5 section 10.3.2
