How to write instructions for a phone AI voice agent

Why the instructions matter more than the voice

People trying an AI voice agent for the first time spend a long time choosing the voice and very little writing the instructions. That is the wrong way round. The voice is noticed in the first three seconds; the instructions decide whether the call ends well, that is, whether the customer gets a correct answer or is passed to the right person.

The instructions (often called the prompt) are a text in ordinary language that the model reads before every conversation. You do not need technical language. What you do need is to be concrete and complete: the voice agent does not know your business, does not know you close on Thursday afternoons and does not know that a certain client must always be put through to the owner, unless you write it down.

A good rule of thumb is to imagine leaving a note for a bright person on their first day at work, who cannot ask you anything. Everything you would tell them in person goes into the text.

The ingredients of good instructions

Instructions that work nearly always have the same six parts. The order matters little; what matters is that none is missing.

1. Who it is and whom it works for

One or two sentences: the name of the business, what it does, where it is. "You answer the phone for Galli Heating, a company that installs and services boilers in Bergamo and its province." Avoid giving the voice agent a fake human identity: it is more honest and simpler for it to introduce itself as the assistant of the business.

2. The goal of the call

This is the most important part and the most neglected. Write down what it must achieve by the end: "Your task is to work out whether the customer has a breakdown, a servicing request or a request for a quote, collect the necessary details and either pass the call on or close with a summary." A voice agent without a goal chats without getting anywhere.

3. The tone

A few precise directions are enough: formal or informal register, short sentences, no long lists read out over the phone. On the phone an answer lasts two sentences at most, then the customer gets to speak. Write this explicitly, because models tend to be wordy.

4. The details to collect

List the details in order and say which are mandatory. Add two rules that greatly improve quality: ask for one detail at a time and repeat the important ones back for confirmation (names, numbers, dates). For phone numbers, it helps to have the digits repeated in groups.

5. What it knows and what it must not do

Write down the facts it may give (hours, address, services offered, documents to bring) and, separately, the prohibitions. Typical prohibitions: do not make up prices or availability, do not give diagnoses or professional opinions, do not promise response times, do not ask for sensitive data that is not needed. Always add the sentence: "If you do not know the answer, say so and offer to put the call through or to arrange a callback."

6. When to hand over to a person

Define the cases in which the call must go to a person: the customer asks for it, is angry, there is an emergency, the request does not fit any planned case, the voice agent has not understood after two attempts. Also say what to do if nobody is available: take contact details and promise a callback, without inventing timescales.

A template to copy

This template sums up the six parts. Copy it, fill in the square brackets and delete the lines you do not need.

WHO YOU ARE
You answer the phone for [business], [what it does] in [city].
You introduce yourself as the assistant of [business].

GOAL
Work out whether the caller wants [case A], [case B] or [case C].
For each case collect the details below and then [put the call through / close with a summary].

TONE
Use a formal register. Short sentences, two per answer at most. No lists.

DETAILS TO COLLECT (one at a time, repeat back for confirmation)
1. First name and surname
2. Phone number for a callback
3. [specific detail: number plate, case number, date]
4. Reason for the call in brief

WHAT YOU KNOW
- Hours: [days and times]
- Address: [address]
- Services: [short list]

YOU MUST NEVER
- Make up prices, availability or timescales
- Give [medical / legal / technical] advice
- Ask for details that are not needed

HAND OVER TO A PERSON IF
- The customer asks for it
- There is an emergency: [concrete definition]
- You do not understand the request after two attempts
If nobody answers: take contact details and say someone will call back.

Three complete examples

The examples are fictional but realistic. Notice how each example defines an emergency in concrete terms, instead of leaving it open to interpretation.

An accountancy firm with four professionals

You answer the phone for Ferraris & Associates, accountants in Turin.
You introduce yourself as the firm's assistant. Use a formal register, short sentences.

Goal: find out whom the customer wants and why, collect the details
and pass the call to reception. Do not book appointments yourself.

Collect, one at a time:
1. First name and surname, or the company name
2. Whether they are already a client of the firm
3. The professional they want, if they know (Mr Ferraris, Ms Conti,
   Mr Riva, Ms Morelli)
4. The subject in one sentence (tax return, bookkeeping,
   payroll, registering as self-employed, other)

What you know: the firm is open Monday to Friday, 9-13 and 14:30-18.
Via Roma 12, second floor. For new clients the first meeting is
arranged by reception.

You must never: give tax advice, mention deadlines or amounts,
say whether a professional is in the office or on holiday.

Put the call straight through to reception if: the customer mentions a tax
demand, a tax audit or a deadline within 48 hours,
or asks for a person. If reception does not answer, take
a number and say the firm will call back.

A boiler servicing company

You answer the phone for Galli Heating, boiler installation and servicing
in Bergamo and its province. You introduce yourself as the company's assistant.
Use a formal register, short and simple sentences.

Goal: tell apart a breakdown, an annual service and a quote.

For a breakdown collect: name, town and address, phone number,
boiler brand if they know it, what is happening (will not start,
leaking water, error code on the display).
For a service: name, town, phone, preferred month.
For a quote: name, town, phone, type of work.

What you know: we only work in the province of Bergamo. Office hours
are 8-12 and 13:30-17:30, Monday to Friday.

You must never: say when the engineer will arrive, give prices, suggest
DIY repairs.

Emergency: smell of gas, water coming out in large amounts, no heating
with elderly people or small children at home. For a smell of gas, immediately
tell them to turn off the gas tap, leave the house and call 112,
then put the call through to the on-call engineer.

A gym with classes and memberships

You answer the phone for Equilibrio Gym, at Via Verdi 40 in Padua.
You introduce yourself as the gym's assistant. Use an informal, friendly tone,
short answers.

Goal: answer questions about opening hours and classes and take
requests for a trial session.

What you know: open Monday-Friday 7-22, Saturday 9-18, closed on Sunday.
Classes: pilates (Mon and Wed 18:30), functional training (Tue and Thu 19), yoga
(Sat 10). The trial session is free and must be booked.

For a trial session collect: name, phone, class, preferred day.
Say that reception will confirm with a message.

You must never: quote membership prices, give advice on
diets, injuries or personalised training.

Hand over to reception if: they want to cancel or suspend a membership,
have a complaint, ask for an instructor by name.

Opening, closing and edge cases

Besides the instructions themselves, there are three moments in the call that are worth writing word for word, because the customer always hears them.

The opening line

This is the first thing the caller hears, and in a few seconds it must tell them whom they are talking to and that they can explain in their own words what they need. "Galli Heating, this is the automated assistant. Please tell me what you need." Avoid long openings listing your services: the customer waits for it to end and grows impatient in the meantime. Stating straight away that it is an automated assistant is also a matter of fairness towards the caller.

The closing line

Every call must end with a summary of what will happen next: "I have made a note of that, Mr Bianchi. We will call you back on 345 218 0937 during office hours tomorrow." The summary lets the customer correct a wrong detail before hanging up, and it is the last useful check on the quality of the data collected.

Edge cases

Think in advance about the calls that fit no pattern and decide what to do with them:

• Sales calls from suppliers or salespeople: take name and company and close politely, without passing them to staff.
• Silence or unintelligible audio: ask once whether the customer is there, then close with a polite sentence.
• Personal questions about the voice agent ("are you a robot?"): answer honestly that it is an automated assistant and go back to the goal.
• A customer who only wants information already in the instructions: give the answer and ask whether they need anything else, without collecting data that is not needed.
• Calls from a withheld number: always ask for contact details, because the system will not give you them.

These cases take up a few lines in the instructions but avoid most awkward conversations. In businesses with a front desk, such as a garage, they are also the calls that waste the most time at the counter: you will find a concrete example in the guide on VoIP for car repair shops.

The mistakes we see most often

Most problems come from a few causes, always the same ones.

• Instructions that are too generic. "Be kind and help the customer" says nothing about what to do. The result is a polite conversation that leads nowhere.
• Too much information to read out. Pasting in the whole price list or the terms and conditions makes the voice agent recite them over the phone. Better a little precise information and, for everything else, a handover to a person.
• No ban on prices. If a price is not written down, the model may estimate one. It must be explicitly forbidden.
• Emergency not defined. "If it is urgent, put the call through" leaves the decision to the model. Every customer will say it is urgent.
• No way out. A flow that does not say what to do when the voice agent does not understand produces calls that go round in circles.
• Contradictory rules. "Do not give information about prices" and, a few lines further down, "a visit costs 60 euros". The model will pick one of the two, and you do not know which.
• Asking for too many details. More than four or five questions on the phone tire the caller, who hangs up.

How to test it before going live

You test a voice agent by actually calling it, not by reading the instructions. Organise a test session with two or three colleagues.

1. Write a list of 10-15 typical calls, taken from real requests in recent weeks: the most common ones, two or three difficult ones, an aggressive one, an off-topic one.
2. Have colleagues call from their mobiles, not from a computer, and in real conditions: in the car, with noise, speaking quickly.
3. For each call, note whether the goal was achieved, whether the details collected are correct and whether there was a handover to a person when one was needed.
4. Read the transcripts of the conversations that went wrong and change one rule at a time, so you can see which change had an effect.
5. Repeat the failed calls until they all pass.
6. In the first two weeks of real use, reread a few conversations every day.

In the AI voice agent of our partner robottino.ai's virtual PBX you can make test calls from the browser and reread the conversation log. To check quality over time across many calls, robottino.ai's AI call analysis lets you search automatically for, say, the conversations in which the customer asked for a person and was not put through.

Instructions for the Vohippo AI secretary

If you do not have a PBX and use the Vohippo AI secretary, the same rules apply in a shorter form. The secretary already collects name, contact details, reason and urgency on its own: in the «What it should ask or say» field, add only what is specific to your business, for example "Also ask for the vehicle's number plate" or "Do not give information about prices".

The decision about what to do with the call stays with you: you receive the card with the summary and the transcribed conversation, and you choose «Accept» or «Reject». If you want a voice agent that decides on its own where to send the call, with queues and menus, you need a full PBX, as described in the guide to the AI virtual PBX.

For examples of flows designed for a specific sector, see the AI PBX examples by sector, or the page on VoIP for professional firms. If you are unsure which solution is right for you, write to us from the contact page.

Frequently asked questions