The difference between an AI agent that callers like and one they hang up on is rarely the technology. It is the script: what the agent says first, what it is told to do, and what happens when it does not know the answer. This guide walks through each part.
1. The opening line
The opening line is said on every call, so it is worth getting right. It should:
- Name the business
- Say the caller is speaking to an AI assistant
- Invite the caller to speak, ideally with a hint of what you can help with
“Thanks for calling Northgate Physio. I’m the clinic’s AI assistant — I can book, move or cancel appointments, or answer questions. How can I help?”
Keep it under about 12 seconds. Callers want to get to their reason for calling.
2. The instructions (system prompt)
This is where you describe the agent’s job, as you would brief a new receptionist. Write in plain sentences:
- Who it is: “You are the receptionist for Northgate Physio, a physiotherapy clinic in Leeds.”
- What it does: “You book, reschedule and cancel appointments and answer questions using the clinic’s documents.”
- How it speaks: “Be warm, brief and professional. Use British English. Ask one question at a time.”
- What it must never do: “Never give medical advice. Never quote a price that is not in the documents. Never promise a call-back time.”
Short sentences work better than long paragraphs. Voice is not chat: answers should be one or two sentences, not lists.
3. Write for the ear
- Spell out how to say things: “Say the phone number in groups, for example 0113, 496, 0000.”
- Avoid symbols and abbreviations the voice might read badly
- Ask the agent to confirm important details back: dates, times, names and numbers
4. Decide what to capture
List the fields your team needs from each call, such as name, phone number, reason for calling and preferred callback time. In Narvin these become captured fields: they appear in call logs and can be sent to your systems by webhook when the call ends. Ask for them naturally through the conversation rather than as a form.
5. Fallbacks and escalation
Every agent meets a question it cannot answer. Tell it exactly what to do:
“If you do not know the answer or the caller asks for a person, say you’ll pass the message to the team, take their name and number and the best time to call back.”
Put this in the agent’s instructions or rules, so it applies on every call.
6. The closing line
End every call cleanly: summarise what was agreed and what happens next.
“So that’s you booked for Wednesday at 4pm with Sarah. You’ll get a confirmation shortly. Thanks for calling Northgate Physio — goodbye.”
7. Test, read, improve
Make ten test calls with realistic scenarios — a booking, a reschedule, an unusual question, an interruption, silence — and read every transcript. Most improvements come from adding one sentence to the instructions or one fact to the knowledge base.
A starter template
You are the AI receptionist for [business], a [type of business] in [town]. You help callers to [main jobs]. Be warm, brief and professional. Use British English. Ask one question at a time and confirm dates, times and phone numbers back to the caller. Answer only from the business documents. If you are not sure, say so and offer to take a message. Never give [medical / legal / financial] advice, never quote prices that are not in the documents and never promise a call-back time. Before ending, summarise what was agreed.
Next, read how to set up an AI phone agent in a day.
