A voice agent is only as good as its brief. The difference between an assistant that sounds like your best consultant and one that sounds like a chatbot reading a script is almost entirely in how you write the instructions. These are the patterns that have held up across travel deployments.
Start with the job, not the personality
Before you write a word about tone, define the outcome. For a sales assistant that might be: capture travel dates, departure airport, destination, party composition, budget band and contact preference; confirm the relevant policy; then book or hand over. Write those outcomes as a checklist at the top of the prompt. Everything else serves them.
Tone that matches your brand
Keep tone rules short and concrete. 'Warm and efficient' means nothing to a model; 'use the caller's first name once, keep answers under two sentences unless asked for detail, never use the words premium or bespoke' does.
Read the transcript of your best human call and borrow its habits — the way it confirms back, the way it slows down for numbers, the way it closes.
Policy lives in the knowledge base, not the prompt
Fare rules, cancellation terms and supplier conditions change. If they live in the prompt they go stale and bloat the context. Put them in retrievable documents and instruct the assistant on when to consult them: 'before quoting a change fee, look up the current policy for this supplier and read the relevant line back to the caller'.
Reusable patterns worth copying
- Confirm-back: repeat dates, names and reference numbers before acting on them
- Graceful interruption: stop speaking the moment the caller does, then resume from the point of interruption
- Honest uncertainty: 'I don't have that detail — I can check with the team and call you back' beats guessing
- Handoff phrase: a fixed sentence that tells the caller a person is joining and what has already been captured
- Numbers aloud: read long references in groups of three or four
Test with real calls, not a demo script
Build a regression set of thirty realistic scenarios — including the awkward ones: a caller who changes their mind twice, background noise, a strong accent, a question outside scope. Re-run it after every prompt change. A prompt that passes the demo and fails the regression set is not finished.
Write the brief you would give a new consultant on their first day, then cut it in half.
