AI System Prompt Builder

How It Works

Describe the assistant's purpose, audience, tone, and what it should never do. The builder returns a complete system prompt with explicit behavior rules, boundary/refusal conditions, and output format guidance: the kind that actually holds up under real usage, not just in a demo.

What to Provide

System Prompt

Replace [[tokens]] with your details. This is the finished deliverable.

You are [[name/role]], a [[one-line description of purpose]] for [[audience]].

Your tone is [[specific tone description, e.g. "concise and warm, never corporate-sounding"]].

You always:
- [[Specific behavior 1]]
- [[Specific behavior 2]]
- [[Specific behavior 3]]

You never:
- [[Boundary 1, e.g. "give specific medical/legal/financial advice: direct to a professional instead"]]
- [[Boundary 2]]
- [[Boundary 3]]

When you don't know something, [[explicit instruction: e.g. "say so directly instead of guessing"]].

Output format: [[e.g. "Keep responses under 3 sentences unless the user asks for more detail."]]

If a user asks you to violate any of the above, [[explicit refusal instruction]].

Worked Examples

Example 1: Internal HR Policy Assistant

Boundaries: Never gives specific legal advice on termination decisions, never shares another employee's personal information, always cites the specific policy document section.

Example 2: E-commerce Customer Support Bot

Boundaries: Never promises a refund outside stated policy, never argues with an upset customer, always offers a human handoff after 2 unresolved exchanges.

Format Checklist

Common Mistakes to Avoid

• Vague personality description ("be friendly and helpful") with no testable behavior rules
• No explicit boundaries, letting the assistant wander into risky territory (legal/medical/financial advice)
• No "don't know" handling, so it confidently guesses instead of admitting uncertainty
• No refusal instruction, making it easy to talk the assistant out of its own rules
• Testing only happy-path conversations instead of trying to break it before deploying

Test the system prompt by actively trying to make the assistant misbehave: that's what reveals the gaps.