"You are an experienced tax accountant…" is one of the most common prompt openings. It can help, but its effects are often overstated.
What Roles Do Well
- Set tone and register: a friendly tutor versus a formal consultant.
- Focus attention: a "security reviewer" looks for vulnerabilities; an "editor" looks for clarity.
- Define perspective: answer as a customer, a critic, a beginner.
- Frame an assistant's job in a system prompt for a whole application.
What Roles Don't Do
A role doesn't give the model knowledge it lacks, make it more accurate on facts, or replace specific instructions. "You are a world-class lawyer" doesn't make legal answers reliable.
Make Roles Concrete
Instead of "You are an expert marketer", describe the job: "Review this landing page as a conversion-focused marketer. Identify the three changes most likely to increase sign-ups, with reasons."
Use Roles for Critique
Asking the model to review a draft from several perspectives — a sceptical buyer, a compliance officer, a new user — often surfaces useful problems.
Personas in Products
When an assistant has a persona, define its boundaries clearly: what it can and can't help with, and how it handles sensitive requests.