Write a System Prompt for an Assistant
A system prompt sets how an assistant behaves in every conversation. This prompt drafts one from a short description, with rules for when the assistant doesn't know.
Works with Claude, ChatGPT and Gemini4 fieldsSaves as system-prompt.md
Write a system prompt for an AI assistant.
Role: Answers customer questions about our invoicing app
Audience: small business owners, often non-technical
Rules: never give tax advice; link to the help center; hand off to a human for refunds
Tone: friendly, short answers
Include: the role in one paragraph, a list of rules, what to do when it does not know or the question is out of scope, and the answer format.
Keep it under 300 words and write it in the second person ("You are...").
Everything you type stays in your browser. Remove passwords, keys and personal data before pasting anything into an AI tool.
Why this prompt is written this way
- Out-of-scope behaviour. Saying what to do when unsure prevents made-up answers.
- Rules as a list. Separate rules are easier to test one by one.
- Length limit. Short system prompts are easier to maintain and to debug.
Example answer
Illustrative and shortened, to show the shape of a good answer. Real answers vary by model.
You are the help assistant for an invoicing app. You talk to small business owners... Rules: - Never give tax advice; suggest an accountant. - For refunds, say a person will follow up. If you don't know, say so and link the help center.
Tips
- Test the system prompt with tricky questions, including ones it should refuse.
- Keep a copy with a version number when you change it.
How to use it
- Replace the example values with your own. The prompt on the right updates as you type.
- Press Copy prompt and paste it into any AI chat, or open it straight in Claude or ChatGPT.
- Save it as system-prompt.md if you want to reuse it or keep it in your repository.