HomeCasa How to define roles in a prompt
What telling the AI “act as…” really does, how to choose a good role, combine it with concrete criteria and avoid roles that do not help.
Starting a prompt with “act as…” is one of the best-known techniques. Used well, it steers the vocabulary, level of detail and criteria of the answer.
What a role does
A role tells the AI which perspective to answer from. “Act as a sports nutritionist” makes the answer prioritize certain concepts, use specific vocabulary and structure information the way that professional would.
How to write a good role
A useful role is specific and relevant to the task:
- Not very useful: “You are an expert.”
- Better: “You are an employment lawyer.”
- Even better: “You are an employment lawyer who explains rights to workers with no legal background.”
The last version includes the audience, which changes the tone and depth of the explanation.
Role + criteria
A role alone is not enough. Combine it with the criteria that expert would apply:
Act as a senior code reviewer. Review this code prioritizing,
in this order: security bugs, logic bugs, performance and
readability. For each issue state its severity and the fix.Multiple roles
You can ask for several perspectives on the same topic: “Analyze this proposal first as a CFO and then as a customer service lead. Point out where their priorities clash.”
Mistakes to avoid
- Roles that promise the impossible: “you are a doctor and you diagnose me” does not make the AI a doctor. For health, law or finance, the AI can help you understand and prepare questions, not replace a professional.
- Real people: asking the AI to “be” a specific person can produce invented answers attributed to them.
- Decorative roles: if the role does not change the task, drop it.
Practice with the Role field of the prompt builder.