Prompting for Assistants

System instructions are the foundation of every assistant. They define who your assistant is, what it does, and how it behaves – before any conversation even starts.

Good instructions make your assistant predictable and useful. Poor instructions lead to inconsistent, off-brand, or unreliable responses.

The anatomy of good instructions

Think of system instructions as a briefing for a new colleague. Cover these areas:

You don't need all five every time – but covering 3–4 makes a big difference.

Example: A simple assistant

Here's a basic but effective instruction set:

You are an internal communications assistant for a marketing team.

Your job:
- Help draft social media posts, newsletters, and internal updates
- Follow our brand voice: professional but approachable

Rules:
- Never invent statistics or quotes – ask for sources if needed
- Keep posts under 280 characters for Twitter, 150 words for LinkedIn
- If unsure about tone, ask before drafting

Always end drafts with: "Let me know if you'd like adjustments."

This is clear, scoped, and leaves room for the user to guide the output.

Keep instructions short and scannable

Long, dense instructions are hard to follow – for humans and AI alike.

Do:

• Use bullet points and short sentences
• Group related rules together
• Put the most important rules first

Don't:

• Write paragraphs of text
• Repeat the same rule in different ways
• Add rules "just in case"

Set clear boundaries

The best assistants know what they shouldn't do. Be explicit about limits:

• "Don't provide medical, legal, or financial advice."
• "If the user asks about competitors, say you can't comment."
• "Never share internal pricing – redirect to the sales team."
• "If you don't know something, say so instead of guessing."

Boundaries prevent your assistant from going off-script in risky situations.

Tell the assistant how to handle uncertainty

AI models sometimes guess when they shouldn't. Add instructions like:

• "If information is missing, ask the user before proceeding."
• "If you're unsure, say 'I'm not certain' and explain why."
• "List any assumptions you made at the end of your response."

This makes outputs more transparent and easier to verify.

Use examples when helpful

If you want a specific output style, show it:

When summarizing meetings, use this format:

**Date:** [date]
**Attendees:** [names]
**Key decisions:**
- [decision 1]
- [decision 2]
**Action items:**
- [owner]: [task] – due [date]

Examples reduce ambiguity and help the assistant match your expectations.

Test and refine

Your first draft won't be perfect – and that's fine.

Common mistakes to avoid

Quick checklist

Before publishing your assistant, verify:

• Role and purpose are clear in the first 2 sentences
• Tone and style are defined
• Boundaries say what the assistant should NOT do
• There's a rule for handling uncertainty
• Instructions are under 300 words and scannable
• You've tested it with realistic questions