System Prompt Generator
Design the system prompt behind a custom assistant, GPT or agent.
Runs entirely in your browser. Your text is never uploaded.
A system prompt is the standing instruction that shapes how an assistant behaves in every conversation. This tool helps you write a clear one — defining the persona, what it can do, its tone, and the rules and boundaries it must respect.
Use it to configure a custom GPT, a Claude Project, or an agent in your own app. To understand the theory, read our guide on system prompts, and refine the result with the Prompt Optimizer.
How to build a system prompt
Define the persona
Give your assistant a role and, optionally, a name and a domain of expertise.
Set behaviour and rules
List what it can do, choose a tone, and add any guardrails it must always follow.
Generate and deploy
Copy the finished system prompt into your GPT, Project or app configuration.
Frequently asked questions
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Write your next prompt in seconds
Turn a rough idea into a clear, structured prompt any AI can follow. Free, private, and no account needed.