Every good AI assistant starts with good instructions. Whether you're filling in ChatGPT's Custom Instructions, a Gemini Gem, a Claude Project, Grok's custom instructions or the system prompt of a chatbot you're building with an API, the same ingredients make the difference between generic answers and genuinely useful ones. This free system prompt builder guides you through each one. Define the assistant's role and expertise ("You are a senior tax accountant for UK freelancers"), describe the audience, and set the tone and length of answers. Choose a response format such as short paragraphs, bullet points, step-by-step or tables, and add the rules that matter: ask clarifying questions when a request is ambiguous, admit uncertainty instead of guessing, cite sources, use British or American spelling, avoid jargon, or never invent facts. You can also add background context about you or your business and list things to avoid. The tool assembles a clean, well-structured prompt using headings and bullet points, which current models follow reliably, and shows a character count so you can stay within limits like ChatGPT's 1,500-character fields. It's all template-based and runs in your browser, with no AI call and nothing saved.
Build your instructions
Where to paste it
- ChatGPT: Settings → Personalization → Custom instructions.
- Gemini: create a Gem and paste into Instructions.
- Claude: a Project’s custom instructions.
- APIs: the system message.
Tips
- Be specific about the audience; it changes everything.
- Test with a few real questions and refine.
FAQ
What is a system prompt?
Instructions the AI reads before every conversation, setting its role, style and rules.
Is longer always better?
No. Clear, specific instructions beat long ones. Keep what changes the answers you get.
Will the AI always follow it?
Mostly, but not perfectly. Restate important rules in your message when it matters.
Is my text saved?
No. The prompt is built in your browser.
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