AI System Prompt Builder
Craft structured, effective system prompts for any LLM. Fill in each field and get a ready-to-use prompt — works with ChatGPT, Claude, Gemini, and any OpenAI-compatible API.
Define who the AI is and its core expertise
What the AI must never do or always do
1-2 examples of ideal interactions (optional but powerful)
Preview
Fill in the fields on the left to generate your system prompt...
Quick Start Templates
Frequently Asked Questions
What is a system prompt?▼
A system prompt is a set of instructions you provide to an LLM before the conversation starts. It defines the AI's role, behavior, tone, and constraints — shaping every response in the conversation.
What makes an effective system prompt?▼
Good system prompts are specific, not vague. Define the role clearly (e.g., 'You are a senior Python engineer'), set concrete constraints (e.g., 'Never suggest deprecated APIs'), specify output format, and include 1-2 examples if possible.
How long should a system prompt be?▼
For most use cases, 100-500 tokens is ideal. Shorter prompts are cheaper and faster; longer prompts add precision. Avoid padding — every sentence should serve a purpose.
Does this tool work for ChatGPT, Claude, and Gemini?▼
Yes. The generated prompt works as a system message for OpenAI (GPT-4o), Anthropic (Claude), and Google (Gemini). Copy and paste it into the system prompt field or pass it as the 'system' parameter in API calls.
Can I save my prompts?▼
Prompts are stored in localStorage so they persist across browser sessions on the same device. Use the Export button to download your prompt as a .txt file for backup.
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