System Prompt Builder
Fill in the fields below to generate a system prompt — persistent instructions for a custom assistant's persona and rules, distinct from a one-off task prompt.
Generated system prompt
Frequently asked questions
How is this different from the Prompt Builder tool?
The Prompt Builder generates a one-off prompt for a single task. This tool generates a system prompt — persistent instructions that define an assistant's persona and rules for an entire conversation or custom GPT/project, used once when setting up an assistant rather than sent with every message.
Where do I actually use a system prompt?
Common places include a custom GPT's instructions field, a Claude Project's system prompt, or the system parameter when calling an AI API directly — check your specific tool's settings for where persistent instructions go.
Why include things the assistant should never do?
Explicit boundaries are one of the more reliable ways to keep an assistant's behavior consistent across an entire conversation, since without them a model tends to drift toward generic behavior over a long exchange.