How to write a voice agent prompt that works on Indian phone calls

A system prompt for a voice agent does a different job from one for a chat assistant. The caller can't scroll back, can't see a list, and will hang up if the agent rambles. Most problems we see in early agents come from prompts written like chat instructions.

This is the structure that works for us across clinics, D2C brands and lenders.

1. Identity in one line

Say who the agent is and who it works for, in the words it should use on the call:

You are Riya, the front desk assistant at Sunrise Clinic, Gurugram.

Skip personality adjectives. "Warm, friendly, empathetic" changes very little; how you phrase the greeting and the questions changes a lot.

2. One goal per call

Write the outcome you want, not the topics the agent may discuss:

Your goal is to book, move or cancel an appointment with one of our doctors.

Agents with three goals do all three badly. If you need sales and support on the same number, use two agents and transfer between them.

3. The steps, in order

List the steps as short numbered lines. The model follows numbered steps far more reliably than paragraphs.

1. Greet the caller and ask how you can help.
2. Ask which doctor or speciality they need.
3. Check available slots with the check_availability tool.
4. Offer at most two slots at a time.
5. Confirm the slot, the patient's name and phone number.
6. Book it with book_appointment and tell them an SMS is on its way.

4. Language rules

Indian callers switch languages mid-sentence. Tell the agent what to do:

• Reply in the language the caller uses; switch when they switch.
• Say numbers, dates and amounts the way people say them ("saadhe gyarah baje", "four thousand two hundred rupees").
• Keep each reply to one or two short sentences. Ask one question at a time.

5. What not to do

Be specific about the failure modes you care about:

• Never give medical advice. If the caller describes an emergency, tell them to call 112 and end the call politely.
• Never promise a slot before the tool confirms it.
• Don't read out lists longer than two items.

6. How to end

Agents that don't know how to end keep talking. Add a closing step: summarise what was agreed, ask if there is anything else, say goodbye and end the call.

Use variables instead of hardcoding

Anything that changes per call (the customer's name, order number, amount due) should be a {variable} filled from user_data when you place the call. The same prompt then works for every customer:

The customer's name is {name}. Their order {order_id} of {amount} is cash on delivery.

Test with real voices, not text

Read your prompt aloud. If a sentence is awkward to say, it will be awkward to hear. Then talk to the agent in the browser and try to break it: interrupt it, answer in Hindi, give an unexpected answer, go silent. Every surprise is one more line in the prompt.

If you'd rather not start from a blank page, describe the agent to Composer in the console and it will write a first version in this structure for you.